Optical random access memory

ABSTRACT

An optical memory (10) is disclosed in which data is stored in an optical data layer (19) capable of selectively altering light such as by changeable transmissivity, reflectivity, polarization, and/or phase. The data is illuminated by controllable light sources (15) and an array of multi-surface imaging lenslets (21) project the image onto a common array of light sensors (27). Data is organized into a plurality of regions or patches (called pages) and by selective illumination of each data page, one of the lenslets (21) images the selected data page onto the light sensors (27). Light in the data image pattern strikes different ones of the arrayed light sensors (27), thereby outputting a pattern of binary bits in the form of electrical data signals. By selectively and sequentially illuminating different ones of the data regions (pages) on the data layer (19), correspondingly different data patterns are imaged by the corresponding lenslets (21) onto the common sensor array (27), thereby enabling many stored data pages to be retrieved by multiplexing at electro-optical speed.

CROSS REFERENCE TO EARLIER FILED APPLICATION

This application is a continuation-in-part of application Ser. No.07/815,924, filed Dec. 30, 1991, now U.S. Pat. No. 5,379,266, claimedthrough international application PCT/US92/11356, filed Dec. 30, 1992.

BACKGROUND OF THE INVENTION

The invention concerns method and apparatus of optically storing andretrieving mass digital data stored as light altering characteristics onan optical material and providing fast random access retrieval.

Optical memories of the type having large amounts of digital data storedby light modifying characteristics of a film or thin layer of materialand accessed by optical addressing without mechanical movement have beenproposed but have not resulted in wide spread commercial application.The interest in such optical recording and retrieval technology is dueto its projected capability of faster retrieval of large amounts of datacompared to that of existing electro-optical mechanisms such as opticaldiscs, and magnetic storage such as tape and magnetic disc, all of whichrequire relative motion of the storage medium.

For example, in the case of optical disc memories, it is necessary tospin the record and move a read head radially to retrieve the data,which is output in serial fashion. The serial accessing of datagenerally requires transfer to a buffer or solid state random accessmemory of a data processor in order to accommodate high speed dataaddressing and other data operations of modern computers. Solid stateROM and can provide the relatively high access speeds that are sought,but the cost, size, and heat dissipation of such devices when expandedto relatively large data capacities limit their applications.

Examples of efforts to provide the relatively large capacity storage andfast access of an optical memory of the type that is the subject of thisinvention are disclosed in the patent literature such as U.S. Pat. No.3,806,643 for PHOTOGRAPHIC RECORDS OF DIGITAL INFORMATION AND PLAYBACKSYSTEMS INCLUDING OPTICAL SCANNERS and U.S. Pat. No. 3,885,094 forOPTICAL SCANNER, both by James T. Russell; U.S. Pat. No. 3,898,005 for aHIGH DENSITY OPTICAL MEMORY MEANS EMPLOYING A MULTIPLE LENS ARRAY; U.S.Pat. No. 3,996,570 for OPTICAL MASS MEMORY; U.S. Pat. No. 3,656,120 forREAD-ONLY MEMORY; U.S. Pat. No. 3,676,864 for OPTICAL MEMORY APPARATUS;U.S. Pat. No. 3,899,778 for MEANS EMPLOYING A MULTIPLE LENS ARRAY FORREADING FROM A HIGH DENSITY OPTICAL STORAGE; U.S. Pat. No. 3,765,749 forOPTICAL MEMORY STORAGE AND RETRIEVAL SYSTEM; and U.S. Pat. No. 4,663,738for HIGH DENSITY BLOCK ORIENTED SOLID STATE OPTICAL MEMORIES. While someof these systems attempt to meet the above mentioned objectives of thepresent invention, they fall short in one or mere respects.

For example, some of the systems proposed above have lens or otheroptical structure not capable of providing the requisite resolution toretrieve useful data density. The optical resolution of the data imageby these prior lens systems does not result in sufficient data densityand data rate to compete with other forms of memory. Although certainlens systems used in other fields such as microscope objectives aretheoretically capable of the needed resolutions, such lens combinationsare totally unsuited for reading data stored in closely spaced datafields. Another difficulty encountered with existing designs is thepractical effect of temperature and other physical disturbances of themechanical relationship between the data film or layer, the lensassemblies and the optical sensors that convert the optical data toelectrical signals. For example, the thermal expansion effects of evenmoderate density optical memories of this type can cause severemisregistration between the optical data image and the read out sensors.Similar difficulties are encountered in the required registrationbetween the recording process and the subsequent reading operations.Intervening misregistration of the high density optical components cancause significant data errors if not total loss of data.

Accordingly, it is an object of this invention to provide an opticalmass memory having random accessibility in a relatively compact sizecomparable to or even smaller than tape and compact disc storagemechanisms and yet still serving data processing equipment in the samemanner that solid state random access memories move data into and fromthe processor's data bus.

SUMMARY OF THE INVENTION

Data is stored in an optical data layer capable of selectively alteringlight such as by changeable transmissivity, reflectivity, polarization,and/or phase. In the case of a transmissive data layer, data bits arestored as transparent spots on a thin layer of material and areilluminated by controllable light sources. An array of imaging lensletsproject an optically enlarged image of the illuminated data onto anarray of light sensors. The layer of data is organized into a pluralityof regions or patches (called pages) and by selective illumination ofeach data page one of the lenslets images the data page onto the arrayof light sensors. Transmitted page data, in this case light passedthrough the transparent bit locations on the data layer, strikedifferent ones of the arrayed light sensors, thereby outputting apattern of binary bits in the form of electrical data signals. Byselectively and sequentially illuminating different ones of the dataregions (pages) on the data layer, correspondingly different datapatterns are imaged by the corresponding lenslets onto the samephotosensor array, thereby enabling many data pages to be multiplexed atelectrooptical speed onto the common photosensor array image plane.

The data storage and retrieval system of the present invention isembodied in read-only devices, write-only devices, and in read/writeconfigurations as described more fully below in the detaileddescription. A preferred form of the invention is to fabricate the datalayer and lenslet array as a bonded structural unit or card, much like asandwich of different layers of material, to thereby fix the opticaldistances and registration of these elements. This bonded data/lens cardstructure minimizes the adverse optical effects of differential thermalexpansion between the data layer and the lenslets and allows for anexceedingly dense data pattern. A further aspect of this sandwiched dataand lenslet card structure is to immerse the data layer in the spaceadjacent the lenslets in a transparent material of select index ofrefraction relative to air and to the lenslet so as to control the angleof divergence of data image rays emanating from the data layer and stillprovide refractive power at the first surface of the lenslet. Thisimmersion material is preferably also a structural bonding layer made ofa transparent polymer described more fully below. The resultingstructure, which can be fabricated at a relatively low per unit cost,provides an effective way of achieving the imaging power needed tofaithfully form the data image onto the common photosensor array,notwithstanding the very dense, compact arrangement of the data.

Still another aspect of this preferred form of the lenslet array is thatthe first surface of each lenslet, i.e., adjacent the data layer, isaspherically contoured to enhance the optical resolution of theexceedingly small and dense patch of data that is to be imaged. The datalayer and lenslet array together with the transparent immersion/bondinglayer can be fabricated at a cost that allows the structure to be madeand effectively and efficiently used as a replaceable data card.

Further still, the preferred form of the write only and read/writeembodiments of the invention uses the bonded data lenslet structure as ablank data card in the write systems for recording data through thefixed lenslet array. The recording data pattern is thus projected andcondensed by each lenslet onto the selected data layer page of therecord medium.

An additional aspect of the preferred form of the invention is theplacement of a diffractive corrector adjacent the refractive lensletsurfaces opposite the data layer to correct for optical aberrationsintroduced by the lenslet optics in the environment of overlapping dataimage rays from adjacent pages due to the close compact spacing of thedata and lenslets. This diffractive corrector, which may take the formof a diffractive grating or a holographic optical element, is formedwith optical modifying grating or holographic ringlets, eachsubstantially centered on the optical axis of corresponding lenslets andhaving overlapping portions at increasing ringlet radius. As a result,the optical ray bundle leaving each lenslet is diffracted in a mannerthat minimizes effects of various forms of optical aberrations. The dataimage reaching the photosensor plane is therefore sharp, with minimumdistortion in spite of the closely packed multiple lensletconfiguration. In a preferred form of the invention, the diffractivecorrector is followed by a field lens that has a single common apertureencompassing the entire lenslet array and serves to bend the variousrays of light associated with the images of different data pages ontothe common image read out plane of the photosensor array.

Still another preferred aspect of the data layer, lens array andcooperating photosensor array is to arrange the data pages in aclose-packed geometry as contiguous cells, preferably hexagonal inshape. Within each cell the data bits are arrayed in a suitable patternsuch as orthogonal rows and columns. The refractive elements of thelenslets are also preferably cellular in shape to conform to the datapages. Complementing the hexagonal cell shape of the individuallyselectable data pages is the arrangement of the sensor sites on imageddata plane in a correspondingly shaped but substantially largerhexagonal field. The projected image of data bits fills up the hexagonalsensing plane field and makes more efficient use of the lenslet anddiffractive corrector optics given the close spacing of these individualelements.

In association with this preferred cellular configuration of the dataregions or pages and sensor array, the individually energizable lightsources, which may be diode emitters, either laser or LED, or may beother solid state or controllable devices, are likewise preferablyformed in a hexagonal cell pattern. Each light source is ofsubstantially the same shape and configuration as its associated hexagondata region or page. A preferred form of the array of light sources isto pack into each hexagonal shaped light source cell a plurality ofconcurrently energized solid state emitters, thereby producing theillumination energy and area coverage best suited for imaging the datalayer onto the distant photosensor array.

A preferred configuration and several alternative write/readconfigurations of the invention are disclosed. In the preferred form,the read-only assembly is modified to add a write subassembly by using adiagonal beam splitter in the optical read path to accommodate anassembly of data page recording or composing light sources and lightvalves, and imaging optics located to the side of the read optics pathfor injecting a record data image into an entrance pupil of a lenslet(opposite the data layer). During recording, a blank data/lenslet cardis installed in the assembly. An array of write or recording lightsources are disposed at a predetermined distance from a write imaginglens which in turn causes a full page of a data light pattern to beprojected through a wall of controllable light valves which are set openor closed to compose a data pattern. The resulting illuminated data pagecomposed by the light valves is then transmitted toward and reflected bythe diagonal beam splitter in the path of the read optics so that theprojected write image is now in the optical path that includes the fieldlens, diffractive corrector, and lenslet array as described above and iscondensed and recorded on the blank data layer.

Data storage may be by thermal, photochemical or energy storagetechniques. For example, known metallic films such as Tellurium, orphotochemical films such as silver halide, diazo, or other optical datastorage processes such as dye-polymer or magneto-optical are-employedfor this recording operation. The primary advantage of recording throughthe data/lenslet card is the substantial elimination of geometricdistortion due to intrinsic characteristics of the lens system. Also,since the recording process is substantially the reverse of optical readimaging, optimum position registration, thermal stability andreliability are achieved.

Alternative forms of the write/read embodiment are disclosed and includea variation on the forgoing preferred embodiment in which the lightvalves in the subassembly of the recording optics are replaced byreflective light modulators.

Another alternative embodiment of the write/read system is to againplace the recording optics and page composer in a side wall or sidesubassembly of the housing, but using in this case a set of recordinglight sources that are arrayed in the configuration of a data page. Thelight sources are energized according to the desired data pattern foreach page that is to be recorded. An electromechanical mover or servomechanism is used to align an array of microlenses, functioningcollectively as a field lens, to controllably direct the light raybundles of the composed data page light sources for maximizing recordinglight energy through the beam splitter and field lens into a specificone of the lenslets which in turn condense and image the composed datapage onto the data layer for recording. A plurality of light shutters,such as an LCD array, are preferably interposed in front of the lensletarray in this embodiment in order to open the optical path for only asingle lenslet at a time and to block stray light rays from enteringadjacent lenslets.

In the read-only and write/read assemblies, the sensor array ispreferably provided by a layer of charge coupled devices (CCD) arrayedin the pattern of the projected data page and causing the data lightimages to generate charge coupled data that is then outputted into databucket registers underlying the photosensitive elements of the chargecoupled devices. Alternatively, other output sensor arrays may beemployed, including an array of photosensitive diodes, such as PIN typediodes.

Another preferred aspect of the disclosed embodiments of the inventionis to provide means for adapting (changing) the light threshold thattriggers each photosensor site to switch binary state, e.g., from a "0"to a "1" output bit signal. A preferred form of such adapted thresholdis a network of cross-coupled biasing resistors for variably biasingeach sensor switching threshold as a function of light sensed atneighboring sensor sites. The biasing resistors are weighted dependingon the proximity to the subject sensor site.

An alternative form of the invention, preferred for certainapplications, combines photosensors and emitters interspersed on thesame plane that receives the read image. The sensors read the data imageas above. The emitters on the sensor plane are used in a write mode tocompose a data page that is to be recorded and the composed page is thenimaged back through the optics (reverse from read) tow rite the dataonto selected pages of the data layer using light blocking shutters inthe path to screen off the non-selected pages.

It is therefore seen that the present invention provides an enormousdata storage capability having random access speeds that approach, ifnot exceed, the fastest solid state RAMs and ROMs. Moreover, theorganization of the data output capability of the present inventionenables unusually large data words to be accessed virtually at the sameinstant, such as at a single clock time. Since the entire data page,when imaged on the photosensor array, conditions the array to output allof the data from that page at any given instance, the size of the outputword is limited only by the number of bits in the sensor array and theaddressing electronics cooperating with the sensor array. Since thearray itself can be interrogated along rows and columns of data, each ofwhich may be on the order of 1,000 bits per row or column, this allowsthe system of the present invention to output a data word on the orderof 1,000 bits, or selected and variable portions thereof as needed. Suchrelatively large output words provide important applications of thepresent invention to such systems as computer graphics, "correlationengines" of computer based industrial systems, and other computerized ordigital based systems.

These and other features, objects, and advantages of the invention willbecome apparent to those skilled in the art from the following detaileddescription and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view, partly cutaway, of a write/read embodimentof the invention showing a housing for the various electrical andoptical components of the optical random access memory of the presentinvention.

FIG. 2 is a full section view in elevation of the optical memory of FIG.1.

FIG. 3a is a section view in elevation of an embodiment of a read-onlyoptical memory in accordance with the present invention.

FIG. 3b is an isometric view of a preferred assembly of multiple opticalmemory modules mounted on and electronically connected via a plug-inprinted circuit interface and module support board.

FIG. 4 is a plan view showing schematically the layout of individuallyswitchable light sources for illuminating data regions or pages duringreadout and showing the arrangement of such light sources as contiguoushexagonal cells.

FIG. 5 is a plan view similar to FIG. 4 showing the layout of the datalayer and FIG. 5-1 is a blow-up of one of the hexagonal data pages ofthe layer depicting the orthogonal array of rows and columns of databits within a single data page.

FIG. 6 is a plan view similar to FIGS. 4 and 5 showing the array oflenslets in a hexagonal cell pattern that cooperates in a one-to-onelenslet to page registration with the hexagonal data layer pattern shownin FIG. 5.

FIG. 7 is a plan view of the diffractive corrector that is disposedadjacent the lenslet array on the side opposite the data layer foroptically modifying and correcting the image rays projected by theindividual lenslets as described more fully in the detailed descriptionand FIG. 7-1 is an enlarged view of a fragment of the corrector.

FIG. 8 is a plan view of the rectangular field lens that encompasses theentire field of data page image rays available from the lenslets of FIG.4 and directs such image rays to a common sensor plane.

FIG. 9 is a plan view showing the layout of the photosensors at theimage sensing plane but depicted schematically at a greatly reduceddensity for illustration purposes.

FIG. 10a is a section of the bonded structure of the data layer andlenslet array usable as a replaceable data storage card or unit.

FIG. 10b is an enlarged fragment view of the lenslet and data layer ofFIG. 10a.

FIG. 10c is another section similar to FIG. 10a showing the arrangementof the data layer and lenslet structure mounted in registration and inface-to-face proximity with the multiple read light sources, in thisinstance LED sets, serving as the read illumination for the embodimentsof FIGS. 1-3.

FIG. 11 is a schematic diagram of the optical characteristics of certaincomponents of the embodiments of FIGS. 1-3 showing light rays emergingfrom the plane of the data layer and passing through an immersionpolymer layer, then through a registering lenslet and hence through atwo surface diffractive corrector.

FIG. 12 is a diagramatic view similar to FIG. 11 but showing theoverlapping of the various data bit rays from a pair of adjacent datapages of the data layer and the associated lenslets, followed by theoptical treatment of the diffractive corrector.

FIG. 13 is an enlarged schematic view of the arrangement and interactionof certain principal components of the invention including the data/lensbonded structure, the diffractive corrector, a field lens and thephotosensor array, and showing the optical paths of data bit light raysfrom the data layer enlarged and imaged on the sensor array through thevarious optical components.

FIGS. 14a and 14b are block diagrams, respectively, of the data writeaddressing and control, and data read addressing and control electronicsassociated with the memories of FIGS. 1, 2 and 3.

FIG. 15a, 15b and 15c are various structural and circuit schematicdiagrams of the preferred embodiment of the sensor array and associatedelectronics.

FIG. 16a, 16b and 16c show various structural components of data writesubsystems of the write/read memory of FIG. 1 and 2.

FIG. 17 is an alternative embodiment of a write/read system in a sectionview similar to FIG. 2, using many of the same elements as the abovebriefly described embodiments but having reflective light modulators tocompose the data page during a write (recording) mode.

FIG. 18 is another alternative embodiment of a write/read system in asection view similar to FIGS. 2 and 17, in which the data page isrecorded by composing it on an array of selectively energized datarecord lights and then imaging that composed page onto the data layerthrough an array of micro lenses and individually selectable LCD lightshutters and employing a set of electromechanical movers to variablyposition the micro lens array for optimum recording light imaging.

FIG. 19 is a plan view of the micro lenses and associatedelectromechanical movers used in the write mode of the embodiment ofFIG. 18.

FIG. 20 is another plan view similar to FIG. 19 showing the pattern ofcomposed data during write operation of the system of FIG. 18, depictedat greatly reduced density.

FIG. 21 shows an alternative embodiment for reading data similar to FIG.13 but differing in that the refractive field lens has been omitted andits function of bending image rays is replaced by a modified diffractiveelement that both corrects and functions as a field lens.

FIG. 22 shows a further alternative embodiment using the field lens butwithout the diffractive corrector.

FIG. 23 is a section view of an alternative write/read embodiment havinga composite of interspersed photosensors and photo emitters on a commonsubstrate at the read image plane for composing recording data pages atthe same plane as the read image data is sensed.

FIGS. 24a and 24b are fragmentary plan views of the circuit layout ofthe combined photosensor and emitter array of the alternative embodimentof FIG. 23, in which FIG. 24b is an enlarged plan view of one compositesensor-emitter site of the many sites shown in FIG. 24a and illustratingthe adapted threshold network and interconnect leads integrated into acommon large scale integrated (LSI) circuit.

FIG. 24c is a circuit schematic of the adaptive threshold sensor networkintegrated into each sensor site on the LSI circuit of the embodiment ofFIGS. 23, 24a and 24b.

FIG. 25 is a schematic diagram similar to FIG. 11, of an alternativeoptical system for use in the embodiments of FIGS. 1-3 in which thecomposite refractive-diffractive surfaces of the lens system arereplaced by a system of first and second diffractive surfaces interposedby a color correction anomalous lens.

FIG. 26 is an enlarged schematic diagram of the lens system of FIG. 25showing the anomalous color correction lens in its preferredconfiguration FIG. 27 is an element.

FIG. 27 is an overall schematic view of the optical system of thealternative embodiment shown in FIGS. 25 and 26 showing the data layer,first diffractive surface, anomalous lens element, second diffractivesurface, and the field lens for imaging the data on the-distal sensorplane.

FIG. 28 is a view similar FIG. 27 showing an alternative embodiment ofthe optical system in which the second diffractive surface of the lenssystem is placed on the first refractive surface of the field lens.

FIG. 29 is a view similar to FIGS. 27 and 28 showing still a furtheralternative embodiment of the optical system using all diffractivesurfaces including a diffractive field lens and incorporating the colorcorrecting anomalous lens element between the first and seconddiffractive surfaces that form the lens system objective.

FIG. 30 is a view similar to FIG. 26 above showing an all diffractivelens system including the color correcting anomalous element and furtherincorporating a shutter LCD layer for shuttering light rays to and fromeach data page for recording and reading functions.

FIG. 31 is an overall schematic view on a reduced scale of the alldiffractive shuttered lens system of FIG. 30 and showing in this viewthe imaging of data bits on the distal sensor plane.

FIG. 32 is a graph of the index of refraction relative to wave length ofa suitable dye used to form the anomalous lens in the embodiments ofFIGS. 25-31.

FIG. 33 sets forth the optical equations used in computing the lensprescription for the color correcting anomalous lens.

FIG. 34 is a diagrammatic view similar to FIG. 12 of the aboveembodiment, but having an alternative configuration of a combinedrefractive and diffractive lens system in which the first objectivesurface is a combination curved refractive element having a diffractivesurface molded thereon followed by a color correcting anomalous lensregion and then a second diffractive surface.

FIG. 35 is an enlarged schematic view of an arrangement of lens elementssimilar in view to FIG. 13 above, depicting an alternative objectivelens system for imaging data through a succession of diffractivesurfaces and interposed variable index gradient lens elements of thelongitudinal gradient type.

FIG. 36 is an enlarged schematic view of an arrangement of lens elementssimilar to the embodiment of FIG. 35 above, depicting a furtheralternative objective lens system for imaging data through a successionof diffractive surfaces and interposed variable index gradient lenselements of the radial variant type.

FIG. 37 is an isometric view of an optical data card read and/or writedevice in a read only configuration.

FIG. 38 is an isometric view of the internal elements of the embodimentshown FIG. 37.

FIG. 39 is a side elevation view of the elements shown in FIG. 38.

FIG. 40 is an alternative embodiment of the device of FIG. 37 in aread/write configuration.

FIG. 41 is a cutaway side view of a data card with a reflective layerutilized in the read/write configuration of FIG. 40.

FIG. 42A is a cutaway isometric view similar to that of FIG. 38 butdepicting multiple data chapters in which each chapter is illuminated bya full chapter light source.

FIG. 42b is an alternative the embodiment of FIG. 42A shown in aread/write configuration.

FIG. 43 is a front elevation view of the embodiment of FIG. 42A.

FIG. 44 is an isometric view of an embodiment featuring a carousel datacard reader.

FIG. 45 is a partial cutaway side elevation view of the embodiment ofFIG. 44.

FIG. 46 is a plan view of a continuous motion data tape reader.

FIG. 47 is a section view of the embodiment of FIG. 46 taken along line47--47.

FIG. 48 is a plan view of an indexed data tape reader.

FIG. 49 is a plan view of one depicting fiducial marks associated with apage of optical data.

FIG. 50 is a cutaway side elevation view of an optical memory module forreading a single chapter of optical data.

FIG. 51 is a cutaway plan view of the module of FIG. 50.

FIGS. 52A through 52E are various views of registration adjustersutilizing wax or polymer filled sheaths.

FIGS. 53A and 53B are views of a registration adjuster utilizing asolenoid.

FIGS. 54A and 54B are cutaway side and plan views respectively of anoptical memory module using springs to bias a single chapter of opticaldata against reference surfaces.

FIG. 55 is a plan view of a 3×3 array of optical data chapters.

FIGS. 56 and 57 are alternative embodiments of the array of FIG. 55.

FIG. 58 is a side elevation sectional view of an array of optical datachapters embodied in a game cartridge inserted into a game player unit.

FIG. 59 is a rear elevation sectional view of the game cartridge of FIG.58.

FIG. 60A is a vertical section view similar to FIG. 18, showing analternative write/read embodiment in which the electromechanically movedmicrofield lens array is replaced by a fixed microfield lens array and adynamic ultrasonic lens module for directing light from each composeddata page to select individual pages on the recording media for writingthe data.

FIG. 60B, 60C and 60D show, respectively, a front elevation view of theultrasonic lens module, a block diagram of the control electronics forthe ultrasonic lens module, and wave form diagrams of the relative phaseof ultrasonic waves launched into the lens module.

FIGS. 61A and 61B are, respectively, a diagrammatic view of analternative embodiment for selecting data pages to be illuminated andimaged on the sensor array by selective coordinated operation ofmultiple page light sources and multiple page LCD shutter module shownin the enlarged, fragmentary isometric view of FIG. 61B.

FIG. 62 is an alternative embodiment combining elliptical LED lightguides for illuminating multiple, but LCD shuttered pages in order toconserve on the number of multiple LED sources while still obtaining theselectivity of one page at a time for imaging on the sensor array.

FIG. 63 is an isometric view similar to FIG. 62, showing an alternativeform of the LED light guide and shuttered page assembly of the typeshown in FIG. 62.

FIG. 64 is still another isometric view similar to FIGS. 62 and 63showing still a further alternative embodiment in which the light guidesfor each LED illuminate one half of a row of arrayed pages and an LCDshutter assembly responds to a command for opening two columns of pages,one column in registration with only one of the sets of LED lightguides.

FIGS. 65A and 65B show, respectively, a vertical cross-section of analternative embodiment and an enlarged fragment thereof forsubmultiplexing each data page by using angled light sources and HOEs(holograpic angle filters) so that only a portion, in this instance onequadrant of a full data page, is selectively imaged on the sensor array.

FIGS. 65C and 65D diagrammatically illustrate how the angled lightsources in conjunction with an HOE filter illuminate selected quadrantsof the full data page onto the sensor array.

FIGS. 66A, 66B and 66C show an alternative embodiment using color lightsources and corresponding color filtering to achieve a functionallysimilar result to the embodiment of FIGS. 65B, 65C and 65D above,respectively,

FIGS. 67A and 67B are, respectively, an isometric cutaway and anisometric diagram of a holographic beam splitter used in a read onlyembodiment in which multiple data chapters forming separate read modulesare selectively arranged on the sides and top of the cubical assembly toimage data from selected pages, one page from any one of the given readmodules onto a common read sensor array.

FIG. 68 is a block diagram of an alternative data output processingscheme for reading the binary data from the sensor array.

FIGS. 69A, 69B, and 69C show an alternative embodiment in which thephoto sensitive elements forming sensor array 27 are overlaid byalternating color and/or polarization filters in order to increase theseparation of sensor bits for improved readout reliability.

FIG. 70 is an enlarged, cross-sectional fragment of the sensor arrayoverlaid by an array of micro-focal plane lenses to refocus and henceconcentrate data image rays onto the sensor elements.

FIG. 71 is a diagramatic view of the optical system embodying analternative field flattener lens overlying the sensor array to enhancethe consistency of the data bit spacing image on the sensor array.

FIGS. 72A, 72B, 72C and 72D are, respectively, a sensor integratedcircuit (IC) layout, an enlarged layout for one sensor bit, a greatlyenlarged IC layout of the single bit detection and logic, and aschematic diagram of the detector and logic for a single sensor cell.

FIGS. 73A, 73B, and 73C are, respectively, a top plan view of a typicaldistribution of sensed data in which the information of bit A coversfour sensor quadrants or elements for reliability and is surrounded bybackground information illustrated as bits B, FIG. 73B is a flow chartof the signal processing of data A (information) and surrounding data B(background) processed from the raw signal outputs developed at thesensor array; and FIG. 73C is a top plan view of a data image withcorner fiducials shown enlarged in FIG. 73C-1 used in the signalprocessing of FIG. 73B.

DETAILED DESCRIPTION

With reference to FIG. 1 and 2, a preferred form of a write/readconfiguration of the optical random access memory 10 in accordance withthe invention is shown to include a housing 11 of a regular polygonshape, in this instance including top and bottom walls 11a and 11b,respectively; opposing side walls 11c and 11d, and front and back walls11e and 11f, respectively. Although not critical to the invention, inthis embodiment the housing 11 is substantially bisected into left andright chambers each of a generally cubical configuration in which theright hand chamber as viewed in FIG. 2 contains the electronics andoptical components for reading data by projecting a data image onto aphotosensor array disposed adjacent the bottom wall 11b at the righthand side of the housing. The left hand chamber of housing 11 containsthe electronics, light sources, and other optics that function tocompose and record data images onto a blank data film or layerpositioned in the right hand chamber as described more fully below.

READ COMPONENTS

To more easily understand the construction and operation of the combinedwrite/read system shown in FIGS. 1 and 2, only those elements of thesystem used for reading data will be described first, then the write (orrecord) elements will be introduced and explained. Thus, with referenceto the right hand side of the bisected housing 11, there is providedadjacent the upper housing wall 11a, an array of light source drivers 13formed in an integrated circuit and coupled by micro leads (not shown)to an array of solid state photoemitter elements serving as the readlight sources 15. Light sources 15 are mounted on a circuit board orother integrated structural unit to fix the sources in a closely packeddense light pattern that will be described more fully in connection withFIG. 4. Immediately beneath and parallel to light sources 15, a unitarydata/lens card structure 17 is removably mounted for storing on a datalayer 19 binary information bits organized in multiple data pages orregions. A complementary lens array 21 is bonded to layer 19 and has aplurality of lenslets disposed in precise, fixed optical registrationwith each multi-bit data region or page. Unitary data/lens structure 17is fabricated as a bonded unit so that the array 21 of lenslets is fixedin spatial relation to the data layer 19 and so that the structure 17 isreadily removable as a unit from housing 11 of the optical memory 10.

To enhance the resolution of the light image rays emanating fromdata/lens structure 17, a diffractive corrector 23 of generally planarshape is located adjacent second surfaces of lens array 21, i.e.,opposite the data layer and first lens surfaces. Following diffractivecorrector 23, the data images projected from data layer 19 and lensarray 21 upon illumination by light sources 15 are further redirected byfield lens 25 having an aperture that encompasses the entire depth andwidth of the right hand chamber of housing 11. Hence, field lens 25 inthis embodiment is of generally rectangular shape about its perimeter asbest shown in FIG. 8 and otherwise has conventional spherical or planooptical surfaces as described more fully herein.

The foregoing elements of the read function of optical memory 10 occupygenerally the upper one third of the right hand chamber of housing 11.Beneath the field lens 25 there is an open cavity that allows for theoptical convergence of the data image rays which in turn form the dataimage onto an upwardly facing common image plane of sensor array 27. Thedata image projected onto array 27 in this preferred embodiment is inthe shape of a hexagon, as is shown in FIG. 9, to conform to the imagegenerating data pages on layer 19, and the light sources and optics;however, the sensor array 27 itself may have a substantially rectangularor, in this case, square perimeter. Beneath sensor array 27 is locatedthe sensor interface circuitry 29 which is preferably fabricated as anintegrated or printed circuit wafer of similar thickness and rectangularperimeter to complement and lie subadjacent sensor array 27 as shown.The free space that would exist between field lens 25 and sensor array27 in which the image magnified by lenslet array 21 is occupied in thisembodiment by a substantially cubical beam splitter 31 having a diagonalbeam splitting plane 31a for cooperating with the writing (record)functions of this optical memory 10 in which a composed record page isgenerated in the left hand chamber of housing 11 and projected inreverse fashion as described more fully below.

Thus, in operation, a single page of binary data selected on data layer19 by energizing a chosen cell of light sources 15, causes a data imageto be generated that appears generally in the shape of the data imageshown in FIG. 9 (although it is depicted at a greatly reduced densityfor illustration). The image has roughly the shape of a hexagon andfills the image plane on the upper surface of sensor array Theindividual data bits within a single data page are here arranged asshown in FIG. 5 in closely spaced rows and columns and at densities thatuse to advantage high resolution optical films and other record mediaincluding but not limited to photochemical films. To provide storagecompetitive with other types of memory, the data bits must be in a sizerange of 2.25 to 0.5 microns and a center-to-center spacing also in thatrange. Each data page is formed by the amount of individual data bitsthat can be collected and grouped into a single hexagon cell as shown inFIG. 5 and at the preferred density range of 2×10⁷ -4×10⁸ bits per cm²,it has been found that about 10⁶ (1 megabit) of data per page (orregion) is an advantageous quantity that results in the generation of adata image after magnification that can be reliably sensed byphotosensitive elements of sensor array 27. In this case, the preferredembodiment provides an optical magnification through the various lensassemblies of approximately 20 to 30 times. Thus, assuming amagnification of 25, the spacing of the projected image elements onsensor array 27 is on the order of 25 microns and a hexagon cellconsisting of a page of data will, in this embodiment, contain onemillion data bits per page that are imaged on a corresponding number ofphotosensitive elements in array 27. The particular structure andoperation of the sensor array 27 and various alternatives to thepreferred embodiment are described in greater detail below. For thepresent, however, it will be appreciated that each data bit which may berepresented by spots of light from the imaged page, causes aphotosensitive element of sensor array 27 to either conduct ornonconduct depending on whether the data is a "1" or a "0" bit. Althoughdifferent forms of data layer 19 may be employed, in the presentpreferred embodiment that data layer 19 is a transmissive mask or filmin which binary "1" bits are transmissive while binary "0" bits areopaque or light blocking.

It will thus be seen that the read elements and operation of opticalmemory 10 provide for accessing each of hundreds of pages of datahaving, for example, one million bits per page at 1 micron bit size. Theread out of data from sensor array 27 is described in greater detail inconnection with FIGS. 14b, and 15a, 15b and 15c; however, it is seenthat by selecting a single data page on data layer 19 by energizing onecell of the LED or laser diode light sources 15 an entire page of 10⁶bits is made available at the interface circuitry 29 associated withsensor array 27 at speeds typical of electro-optical switching, e.g.,equal to or less than 50 nanoseconds. Data words that make up differentportions of the entire page may be addressed, such as a column or row ofdata on each page, or the entire page may be output. Each row or columnof data within an accessed page may contain as many as one thousand databits, hence making fast retrieval of exceedingly long bit words of thismagnitude within the capability of the optical memory 10. In terms ofdimensions, a one million (10⁶) bit page imaged on sensor array 27 willoccupy a hexagon that would fill an area of 6.5 cm² or about 1 squareinch. Similarly, at the above stated preferred density range of 2×10⁷×4×10⁸ bits per cm², an area of 6.5 cm² (about 1 square inch) containsas many as 640 patches or pages of data, each patch or data page beingalmost instantaneously selectable (≦50 nanoseconds) and retrievable bythe high speed switching capabilities of electro-optical and electronicaddressing devices. In effect, the multiple pages of data bits aremultiplexed onto the image plane at sensor array 27 by electronicswitching of read light sources 15. The output data is available in theabove-mentioned form for direct (without buffer storage) application toa processor data bus.

Further details of the construction and operation of the read functionof optical memory 10 will be described in conjunction with a separateread-only system shown in FIG. 3 and the corresponding electronic andoptical components depicted in FIGS. 4-15. It will be appreciated thatthese read function components, used separately in the read-only systemof FIG. 3, correspond to the read elements in the combined write/readoptical memory 10 shown in FIG. 1 and 2 but for the intervening beamsplitter 31.

RECORDING COMPONENTS

Now with further reference to FIGS. 1 and 2, the write or recordingfunction of optical memory 10 is provided primarily by the componentslocated in the left hand chamber of housing 11. These include an arrayof page illuminating light sources 33, light source imaging lens 35, andan array of LCD light valves 37 located substantially at the bisector ofhousing 11 and hence to one side of the read-only optics of opticalmemory 10 described above. The module of recording light sources 33 isformed by an array of light emitters such as LEDs or laser diodesarrayed in a configuration that complements the arrangement of pages ondata layer 19 which, in this embodiment, are in the hexagonal cellularpattern as shown in FIG. 5. Each element of light sources 33 is hencepositioned within the optical path of memory 10 so as to cause light tobe imaged by lens 35 over the entire face of light valves 37 whichcompose a full page of data bits by open or closed condition, onto asingle page of data layer 19. More particularly, the recording image isreflected at the beam splitting diagonal plane 31a of beam splitter 31and is then condensed in reverse optical processing (compared to theread mode) by field lens 25, diffractive corrector 23, and one of thelenslets of lens array 21 that is associated with the selected data pageon layer 19 to be recorded. The geometrical and optical positioning ofthe pattern of light sources 33, when individually energized, cause thedata composed by valves 37 to be recorded onto the selected page oflayer 19.

It is noted that the relative dimensions of light sources 33 aresomewhat smaller than might be expected by comparison with the pages ondata layer 19 and the lenslets of array 21. The dimensions of sources 33can be different from the array of pages on data layer 19 because theimaging process changes magnification through source imaging lens 35. Inthis preferred embodiment, the dimensions of light sources 33, both as acollection of sources and as individual light elements, is one half ofthe size of the pages of the data array on layer 19. A magnification oftwo times is provided by source imaging lens 35 in order to expand theilluminating recording light rays which are then passed by light valves37 into the right hand chamber of housing 11. The data image is thendeflected by beam splitter 31 up into the image condensing pupils oflens array 21 and onto the plane of data layer 19 for recording. Lightvalves 37 are preferably liquid crystal device (LCD) shutters interfacedto the data composing registers (see FIG. 14a) which sets the shuttersaccording to whether the recorded bits are to be transmissive or opaque.Alternatively, light valves 37 may be ferroelectric shutters or otherdevices that alter the light that then fixes the data image on layer 19.Since light valves 37 collectively form a full page of data bits, thereare in this embodiment 10⁶ million light valves fabricated on anintegrated LCD shutter wafer that in turn is mounted as a prefabricatedlayer in the housing 11 as shown. In order to keep the sameobject-to-image size relationship for recording and reading, theeffective recording and reading path lengths should be the safe.

In operation of the optical memory 10 of FIGS. 1 and 2, it will beappreciated that the system may be used for both writing (recording) andreading (data access) operations.

Thus, the recording function of optical memory 10, including the imagingoptics of lens 35, field lens 25, diffractive corrector 23, and multiplelens 21, causes the composed data image in light valves 37 to be reducedin size (on the same principle as a photographic enlarger except inreverse, i.e., making smaller) with the source imaging lens 35 servingas a condenser. The data light rays to be recorded fill the entrancepupil of one of the lenslets of array 21 where the data pattern isfurther condensed and imaged onto the data layer forming layer 19 wherethe data is stored by optical recording processing techniques known perse, such as silver halide, diazo and/or others. The light valves 37 areselectively opened or closed to compose the data page, and serve as thecounterpart of a negative in a photographic enlarger while the datalayer 19 serves as the print paper. As an alternative to theconfiguration of optical memory 10 of FIG. 1 and 2, the data readfunction can be provided by a modification in which the data layer 19 ofstructure card 17 is made reflective rather than transmissive. Areflective record can then be used in conjunction with light sources 33serving both as record lights as described above, and in a read mode asmultiplexed read light sources in place of read light sources 15. Insuch case, during read, a selected one of light sources 33 is turned on,causing a source of illumination to be directed to and reflected off ofa selected page of reflective data on layer 19 and returned through thebeam splitter plane 31a of beam splitter 31 to the sensor array 27 wherethe reflected image would be output by addressing array 27 usinginterface circuitry 29.

READ-ONLY MEMORY

FIG. 3a shows a preferred form of a read-only optical memory 12 for usein retrieving data that has been stored on data layer 19 and moreparticularly on a data/lens array card 17 using a data writing techniquedescribed above in connection with optical memory 10 or prepared byother recording or reproduction processes including mass copyingtechniques such as contact printing. Thus, using read-only opticalmemory 12, a data/lens array card 17 is installed in an optical memoryhousing 14 similar to housing 11 of optical memory 10 but in this casebeing provided by a housing consisting of only the right hand chamber ofthe write/read housing. Using an arrangement of the read electronics andoptical components that is substantially the same as in the read sectionof write/read optical memory 10, read-only optical memory 12 has lightsource drivers 13, light sources 15, data layer 19 and lens array 21constituting card 17, diffractive corrector 23 and field lens 25 allarranged in relatively close-layered relation, if not in face-to-facecontact, in the upper portion of the optical memory housing 14 near topwall 14a as shown. Similarly, adjacent the bottom 14b of housing 14,sensor array 27 is mounted along with the associated sensor interfacecircuitry 29. In this form of the invention, the read data image isretrieved from each page of data layer 19 by multiplexing the arrayedlight sources 15, causing the images to be projected as described forthe read operation, onto the image plane of sensor array 27.

As individual sensor sites on array 27, organized in a data pattern suchas shown in FIG. 9, are either illuminated or dark, depending upon thedata bit, the corresponding sensor element is conditioned to output a"1" or "0" data bit when addressed. As also discussed, the output dataavailable from sensor array 27 through associated sensor interfacecircuitry 29 is at an unusually high data rate in which entire columnand row words on the order of 1,000 bits each are retrievable inparallel at a single clock time. Alternatively, individual bits orpartial words can be retrieved by high speed random access addressing ofarray 27 and circuitry 29 without the constraint of slow speed serialread out typical of other optical memories such as Compact Disc andmagnetic memories including tape and magnetic disc.

Light sources 15 for optical memories 10 and 12 are preferably arrangedin a hexagonal cell 43 pattern as shown in FIG. 4 and FIG. 10c, eachcell being composed of a set of multiple photoemitter diodes 41 in orderto achieve the required intensity of the illuminating light per datapage. Thus, during data read out, each cell of light sources 15 isturned on by multiplexing data retrieval circuitry shown in FIG. 14b,firing all the emitter diodes 41 in a given cell for a read out timeinterval sufficient to condition the photosensor array. Preferably,diodes 41 are laser diodes which have a more intense emission; however,LED diodes may be used in many applications.

The light emitting faces of diodes 41 and hence cells 43 are located ona light emitting interface plane 44 as shown in FIG. 10c and it is atthis interface plane 44 that the data/lens array card 17 is placed inclose proximity to the light sources with the data layer 19 adjacentinterface 44. In the preferred form of optical memories 10 and 12, card17 is replaceable. By incorporating guides that accommodate sliding thecard sideways into the housing 14 through an access door at the frontwall (see FIG. 3b) of housing 14, cards with different data are quicklyexchanged. Light source drivers 13, light sources 15, diffractivecorrector 23, field lens 25, sensor array 27, and its interfacecircuitry 29 are all securely mounted in housing 11 of optical memory 10and housing 14 of optical memory 12 and are not usually replaceable.

FIG. 3b shows a plurality of read-only memory 12 modules each providedby one of the read-only optical memories of FIG. 3a. These are mountedon a plug-in memory board 40 having an edge connector 42 with multi-leadconductors to the memory module interface and driver circuits. Eachmemory module 12 has a front card receiving slot 46 opening to precisioncard positioning edge guides 48 (see FIG. 3a) for receiving areplaceable data/lens card 17 as described above.

Now the fabrication of data/lens card 17, and more particularly, theconstruction of the lenslets of array 21 will be described withreference to FIGS. 10a-e, 11, 12 and 13. In configuring the lenslets ofarray 21, the shape of the data pages shown in FIG. 5 must beconsidered. Of course, there needs to be some empty space between datapages of the layer 19 in order to prevent interference (cross-talk)between data in adjacent pages. Because a lens is generally axiallysymmetric, its optimum imaging capability is in a circle, so a squarearray of bits is not optimum. That is, for a given refractive lenscomplexity in terms of its contouring and the cost of fabricating such alens, there is a maximum circular area that will be imaged to maximumresolution, and the cost/complexity of a lens will increase dramaticallyas the radius (field of view) increases, assuming other parameters areheld constant.

The most efficient use of each lens subsystem in array 21 is to make thedata array, i.e., the pages of data layer 19, circular so that thediameter of each data field makes maximum use of the available lensimaging power. However, if the lenses and data patches are arranged in aregular array of columns and rows, there will be a significant fractionof area lost in the corners between the circular data regions.

With this in mind, the present invention is preferably embodied byforming each of pages 47 of data layer 19 in a close-packed cellularpattern, here each cell being hexagonal as best shown in FIG. 5. Eachcell is filled substantially by the data bits at a uniform density asindicated by the enlarged fragmentary view of a single cell page 47' inFIG. 5. Thus the cellular shape of the data pages 47 serves toaccommodate maximum density of data and efficient use of the circularconfiguration of lenses. Since the data pages are of hexagonal profilethen the preferable configuration of the light source cells 43 of lightsources 15 is also hexagonal to complement the hexagonal shaped andarrayed data pages. Given this preferred configuration of data pages 47,light illuminating sources cells 43, lenslets 51 of array 21, and theprojected data image on the sensor array 27, a single data page containsone million bits each of approximately 1 micron size organized into 640pages, each page being about 0.8 to 1.0 mm in diameter, for a totalstorage capacity per data/lens card 17 of 640 megabits and 80 megabytes(assuming 8 bit words per byte).

LENS CONSTRUCTION

Now in order to resolve data bits on layer 19 of required size anddensity, namely, between 2.25 and 0.5 microns, preferably about 1micron, and stored at 2×10⁷ to 4×10⁸ bits per cm², the numericalaperture (NA) of each lens subsystem of array 21 must be relativelylarge, in the range of about 0.35 to 0.6, and preferably approaches 0.6for 1 micron bit size. The focal length of the lenslet should be 1.0 mmor less and the spacing of the first lense surface to the data layeralso should be 1.0 mm or less. Such NA values are normally found only inmicroscope objectives having a large number of elements. Read heads ofCompact Disc systems use high power lenses but they only need to resolveone bit at a time, as compared to the megabit resolution of a field ofdata required by preferred embodiment of the present invention. The useof known Compact Disc objective lens designs will not provide adequateimaging resolution of the small, densely stored data bits on layer 19.Furthermore, it is not practical to adopt directly those multi-elementobjective lenses found in high resolution microscopes because of thecost, physical size and the lateral space requirements of such lensassemblies given the close-packed spacing of the data pages 47 on layer19.

Therefore, in designing each of the lenslets of the lens array 21 inaccordance with the preferred embodiment, data/lens card 17 is composedof a continuous layer of lens glass having the contoured opticalsurfaces of the lenslets molded or otherwise formed thereon in aclose-packed array 21. The first active lens surface 52 of each lenslet51 of array 21 proximate to the data layer 19, i.e., within a distancethat is the same order of magnitude as the diameter of the data field ina page 47. This is best illustrated in FIGS. 10b and 11 in which asingle lenslet 51 shown as a subsystem of array 21 has its first activelens surface 52 (S1) within a spacing s of 1/10 to 3/4 of the fielddiameter of the lenslet (and the associated data page), which is in therange of 0.8 mm to 1 mm. This close optical coupling of surface 52 oflenslet 51 to the plane of the data layer 19 enables each data bit ofthe mask to form light image rays when illuminated by one of sources 15that strike surface 52 of each lenslet at different locations on firstsurface 52. This is indicated by the optical ray patterns of FIG. 11 andFIG. 12 in which extreme data bits 53a and 53c are indicated (onopposite sides of a center bit 53b) to form light rays intersectingsurface 52 at different contours. Secondly, the diameter of the datapage 47 and the field of view of the lenslet 51 are substantially equal,and the first surface 52 (S2) of lenslet 51 is made strongly aspheric.By contouring surface 52 aspherically, the surface provides a uniqueoptical treatment of the ray bundles from diverse data points 53a,b andc. The unique optical treatment is needed to accommodate the relativelylarge field angle due to the close spacing of the lens surface to thedata layer 19 and the fact that the lens diameter is substantially thatof the page 47 which is being resolved.

Thirdly, the optical space between data layer 19 and surface 52 oflenslet 51 is filled with a lens immersion material or spacing layer 55such as a transparent polymer (i.e., plastic) having an index ofrefraction that is greater than air to provide the needed angle of databit light rays to resolve each bit and is different from the index ofthe lenslet material which is preferably glass in order to define thefirst lens surface 52. For example, a glass having an index of 1.75 willwork with a polymer having an index such as 1.5, which is typical ofplastics. Furthermore, a plastic spacing layer 55 not only immerses thedata field on layer 19 in a material having the desired index ofrefraction, but also serves to bond and hence fix the relative opticalspacing of the lenslet relative to data layer 19. Plastic spacing layer55 thus has a thickness s less than the diameter of the lens and datafields. Fabrication of spacing layer 55 may, for example, be spincoated. The lenslets 51 of array 21 are preferably formed of acontinuous sheet of relatively high index glass having on one surfacethe circular aspherical contours that form the first lens surface 52.The second surface of the lens glass layer is formed with the pluralityof second lens surfaces 54 (S2) of lenslets 51 which are here ofsubstantially spherical convex shape in axial optical alignment with theaspherical first surfaces 52 (S2). The thickness of each lenslet 51along the optical axis, and hence the approximate thickness of the glasslayer, is on the order of the same dimension as the field diameter of adata page, namely 0.8 to 1 mm.

Fourthly, the center-to-center spacing of the lenslets is the same asthe center-to-center spacing of the data pages 47 which, because ofgeometrical constraints, means that the second optical surface 54 (S2)of each lenslet 51 is the effective aperture stop. Coaction of first andsecond lens surfaces 52 and 54 provides the primary imaging andaberration correcting optical power of the device.

As mentioned, spacing layer 55 bonds and fixes the optical space betweenthe data layer and the lens array layer. Therefore, differential thermalexpansion and other causes of misregistration and misalignment of theoptics are minimized at the location of maximum optical sensitivity.This resulting sandwich structure that serves as data/lens card 17 isnow usable as a unit in either optical memory 10 for writing andreading, or after being recorded once in memory 10 as a read-only cardin optical memory 12. The resulting data image may be projected directlyonto a photosensor array 27 from the second surface 54 of lenslet 51 asshown in FIG. 11, but in accordance with the preferred form of theinvention, the optical images from the second surface 54 of lenslet 51are further refined through a diffractive corrector 23 having third (S3)and fourth (84) optical surfaces 62 and 64.

This additional optical corrector used in optical memory 10 and opticalmemory 12 and best shown in FIGS. 11 and 12, serves to correct forresidual aberrations in the images projected from the data page in anoptical system in which the light rays emanating from adjacent lenslets51 of array 21 overlap. By using a diffractive corrector 23 that hasoverlapping diffractive ringlets, this embodiment of the inventionprovides additional corrective surfaces for treating overlapping lightrays emanating from adjacent data pages. Beyond the effective aperturestop of the image rays from refractive lenslet surface 54, adjacent datapages enter the same expansion space and the overlapping diffractiveoptics of corrector 23 provide a way of optically changing and hencecorrecting aberrations of these comingled image rays while retaining theintegrity of each page image.

Therefore, diffractive corrector 23, which may be a diffractive gratingof generally round overlapping ringlets or gratings 59 shown in enlargedform 59' in FIG. 7, provides third and fourth surfaces 62 (S3) and 64(S4) to correct the optical data image rays emanating from secondrefractive surface 54 (S2) of the lenslet as best shown in FIGS. 11 and12. More particularly, with reference to FIG. 12, it is seen thatadjacent data pages N and N+1 of data layer 19 cause image light rays(one in solid lines and the other in dotted lines) to overlap after thesecond surfaces 54 (S2) of the adjacent lenslets 51 of array 21. As analternative to the diffractive gratings 62 (S3) and 64 (S4), aholographic plate may be used in place of the grating plate to functionas diffractive corrector 23. The holographic plate would be formed in amanner analogous to the ringlet patterns 59 of the grating shown in FIG.7, by light interference images on a photographic plate using processesknown per es.

The imaging of the data is enhanced by placing each separate data patch(page) on a slightly concave curvature facing the lenslet, as best seenin FIG. 10b, adjacent the first surface (S1) of the lens subsystem inorder to reduce field curvature of the image plane. An example of thiscontouring is given in the following tables as a non-flat surface atSRF=0, being the object surface at the data layer 19. In such case, thedata page contouring is formed by a press molding of the bonding layer55 with a convex or dimple region at each page position prior to formingthe data layer emulsion or film. Alternatively, a flat data page may beused with optics reconfigured to adjust for the flat field of the data.

LENS PRESCRIPTION

The lens system comprising a refractive lenslet 51 having a strongaspheric first surface 52 (S1), a second substantially but not exactlyspherical second surface 54 (S2), and followed by spaced diffractivethird surface 62 (S3) and a diffractive fourth surface 64 (S4)constitute a preferred objective lens subsystem. A minimum of foursurfaces are thus provided in this embodiment with correction foroptical aberrations, such as spherical, coma, distortion, astigmatismand field curvature. Such a lens structure is capable of imaging atsufficiently high resolution the 2.25 micron or smaller data bits. Infabricating the elements of this lens subsystem, several examples aregiven of the optical specifications of each of the four objective orprimary surfaces S1, S2, S3, and S4, as well as the additional surfacesS5 and S6 of the spherical field lens and the contour of the data layerat SRF=0. The first example is for a lens system of the preferredembodiment, including a field lens 25 as shown in the following Table 1in which the first set of data is for the spherical contours and thesecond set of data is the aspheric numbers.

                                      TABLE 1                                     __________________________________________________________________________    LENS SYSTEM USING FIELD LENS                                                  __________________________________________________________________________    LENS DATA, OFF AXIS CASE:                                                     SRF   RADIUS THICKNESS                                                                              APERTURE RADIUS                                                                           GLASS                                       __________________________________________________________________________    0     1.6507 0.34000  0.40000     1.51021                                     1     --     1.0677   0.48000     1.730                                       2     -1.14784                                                                             0.56209  0.48000     AIR                                         3     --     1.00000  1.00000     LASF9                                       4     --     1.00000  2.00000     AIR                                         5     29.72358                                                                             5.00000  14.00000    LASF9                                       6     189.14824                                                                            27.00000 14.00000    AIR                                         7     --     --       12.00000    IMAGE                                       __________________________________________________________________________    ASPHERIC DATA BY SRF:                                                         __________________________________________________________________________    1 P1                                                                              0.41868                                                                             P2 -4.15565                                                                             P3 38.37165                                                                             P4 -375.74267                                     P5                                                                              261.09145                                                                           P6 1.1372E+04                                                                           P7 -4.2733E+04                                            2 CC                                                                              -0.79418                                                                    P1                                                                              0.04666                                                                             P2 -0.22600                                                                             P3 1.48769                                                                              P4 -13.02285                                      P5                                                                              58.52966                                                                            P6 -135.09437                                                                           P7 124.09391                                              3 DFX COEF:                                                                   S1  -0.00018                                                                            S2 0.00663                                                                              S3 -0.26361                                                                             S4 0.00014                                      S5  -0.26272                                                                            S6 0.00020                                                                              S7 -0.00073                                                                             S8 0.00041                                      S9  -0.00058                                                                  4 DFR COEF:                                                                   S1  0.04124                                                                             S2 0.01732                                                                              S3 0.08333                                                                              S4 -0.12804                                     S5  -0.01943                                                                            S6 0.24108                                                                              S7 -0.13212                                                                             88 -0.17595                                     S9  0.12643                                                                             S10                                                                              0.15038                                                                              S11                                                                              -0.18001                                                                             812                                                                              0.05138                                      __________________________________________________________________________    LENS DATA, ON AXIS CASE:                                                      SRF   RADIUS THICKNESS                                                                              APERATURE RADIUS                                                                          GLASS                                       __________________________________________________________________________    0     1.6507 0.34000  0.40000     1.51021                                     1     --     1.0677   0.48000     1.730                                       2     -1.14784                                                                             0.56209  0.48000     AIR                                         3     --     1.00000  1.00000     LASF9                                       4     --     1.00000  2.00000     AIR                                         5     29.72358                                                                             5.00000  14.00000    LASF9                                       6     189.14824                                                                            27.00000 14.00000    AIR                                         7     --     --       12.00000    IMAGE                                       __________________________________________________________________________    ASPHERIC DATA BY SRF:                                                         __________________________________________________________________________    1 P1                                                                              0.41868                                                                             P2 -4.15565                                                                             P3 38.37165                                                                             P4 -375.74267                                     P5                                                                              261.09145                                                                           P6 1.1372E+04                                                                           P7 -4.2733E+04                                            2 CC                                                                              -0.79418                                                                    P1                                                                              0.04666                                                                             P2 -0.22600                                                                             P3 1.48769                                                                              P4 -13.02285                                      P5                                                                              58.52966                                                                            P6 -135.09437                                                                           P7 124.09391                                              3 DFX COEF:                                                                   S1  5.9759E-05                                                                          S2 -0.00018                                                                             S3 -0.28961                                                                             S4 3.0229E-05                                   S5  -0.28958                                                                            S6 0.00012                                                                              87 -7.5216E-05                                                                          S8 0.00037                                      S9  1.0458E-05                                                                4 DFR COEF:                                                                   S1  0.06932                                                                             S2 0.02576                                                                              S3 0.07384                                                                              S4 -0.15970                                     S5  0.23013                                                                             S6 -0.32693                                                                             S7 0.29274                                                                              S8 0.08388                                      S9  -0.32881                                                                            S10                                                                              0.05363                                                                              S11                                                                              0.17927                                                                              S12                                                                              -0.08469                                     __________________________________________________________________________

As an alternative, Table 2 contains the spherical and aspheric data foran embodiment that incorporates the field lens function in thediffractive elements as shown in FIG. 21.

                                      TABLE 2                                     __________________________________________________________________________    LENS SYSTEM WITHOUT FIELD LENS                                                __________________________________________________________________________    LENS DATA, OFF AXIS CASE:                                                     SRF   RADIUS THICKNESS                                                                              APERTURE RADIUS                                                                           GLASS                                       __________________________________________________________________________    0     1.63883                                                                              0.46858  0.40000     1.51021                                     1     --     1.06770  0.48000     1.730                                       2     -1.08912                                                                             0.65696  0.48000     AIR                                         3     --     1.71849  1.00000     LASF9                                       4     --     33.00000 2.00000     AIR                                         5     --     --       12.00000    IMAGE                                       __________________________________________________________________________    ASPHERIC DATA BY SRF:                                                         __________________________________________________________________________    1 P1 -0.02894                                                                             P2 -1.34813                                                                             P3 5.70154                                                                              P4 -78.12907                                    P5 178.56707                                                                            P6 2329.4442                                                                            P7 -1.7700E+04                                                                          P8 3.4026E+04                                 2 CC -0.48711                                                                   P1 -0.01041                                                                             P2 -0.06934                                                                             P3 0.13071                                                                              P4 -0.98380                                     P5 3.41779                                                                              P6 -14.03236                                                                            P7 57.27584                                                                             P8 -138.09144                                   P9 132.08888                                                                3 DFR COEF:                                                                   S1   -0.07525                                                                             S2 -0.0274                                                                              S3 0.01787                                                                              S4 -0.01617                                   S5   -0.00466                                                                             S6 0.02402                                                                              S7 0.00246                                                                              S8 -0.02125                                   S9   -0.01578                                                                             S10                                                                              0.01511                                                                              S11                                                                              0.03259                                                                              S12                                                                              -0.02910                                   S13  -0.00099                                                                             S14                                                                              0.00419                                                        4 DFX COEF:                                                                   S1   -3.2687E-05                                                                          S2 0.15927                                                                              S3 -0.08182                                                                             S4 -2.3305E-05                                S5   -0.08060                                                                             S6 -6.7782E-05                                                                          S7 0.00044                                                                              S8 5.9404E-05                                 S9   0.00039                                                                              S10                                                                              0.01571                                                                              S11                                                                              -3.9553E-05                                                                          812                                                                              0.03137                                    S13  9.6939E-06                                                                           S14                                                                              0.01565                                                                              S15                                                                              2.0557E-05                                                                           S16                                                                              -2.4753E-05                                __________________________________________________________________________    LENS DATA, ON AXIS CASE:                                                      SRF   RADIUS   THICKNESS                                                                            APERATURE RADIUS                                                                           GLASS                                      __________________________________________________________________________    0     1.63883  0.46858                                                                              0.40000      1.51021                                    1     --       1.06770                                                                              0.48000      1.730                                      2     -1.08912 0.65696                                                                              0.48000      AIR                                        3     --       1.71849                                                                              1.00000      LASF9                                      4     --       33.00000                                                                             2.00000      AIR                                        5     --       --     12.00000     IMAGE                                      __________________________________________________________________________    ASPHERIC DATA BY SRF:                                                         __________________________________________________________________________    1 P1 -0.02894                                                                             P2 -1.34813                                                                             P3 5.70154                                                                              P4 -78.12907                                    P5 178.56707                                                                            P6 2329.44442                                                                           P7 -1.7700E+04                                                                          P8 3.4026E+04                                 2 CC -0.48711                                                                   P1 -0.01041                                                                             P2 -0.06934                                                                             P3 1.13071                                                                              P4 -0.98380                                     P5 3.41779                                                                              P6 -14.03236                                                                            P7 57.27584                                                                             P8 -138.09144                                   P9 132.08888                                                                3 DFR COEF:                                                                   S1   -0.15865                                                                             S2 0.00257                                                                              S3 -0.25194                                                                             S4 1.26070                                    S5   -2.86407                                                                             S6 2.37729                                                                              S7 1.36299                                                                              S8 -2.36629                                   S9   1.48033                                                                              S10                                                                              1.20315                                                                              S11                                                                              2.25310                                                                              S12                                                                              0.17190                                    S13  -2.44329                                                                             S14                                                                              -0.03497                                                                             S15                                                                              0.80123                                              4 DFR COEF:                                                                   S1   -0.01076                                                                             S2 0.03052                                                                              S3 -0.04407                                                                             S4 -0.12362                                   S5   -0.16767                                                                             S6 0.07931                                                                              S7 0.04196                                                                              S8 -0.03445                                   S9   -0.02233                                                                             S10                                                                              0.00881                                                                              S11                                                                              0.01273                                                                              S12                                                                              3.4632E-05                                 S13  -0.00673                                                                             S14                                                                              0.00203                                                        __________________________________________________________________________

In computing these spherical and aspherical lens data, including thedata for the diffraction gratings of corrector 23, the prescriptions areestablished using known optical design criteria.

Conventionally, a lens with an aspheric surface, or with a diffractivesurface, is described with a power series. In the present case, allaspheric surfaces are axially symmetric, and the sag of the surface,i.e., the location of a surface point along the optical axis, as afunction of the distance R from the axis, is given by: ##EQU1## wherethe P_(M) coefficients are specified in a lens prescription. The term Cis the basic curvature of the surface, and K is the conic constant ofthe surface.

Diffractive surfaces are described by a similar equation, where it isthe relative phase of the light that is given, as a function of theposition on the lens surface. In the present case, both axiallysymmetric (DFR) and general (DFX) surfaces are used. In the symmetriccase, the phase is given by: ##EQU2## It is the S_(M) coefficients thatare specified by the prescription.

The general case is more complex mathematically, and is given by therelationships: ##EQU3## CONTROL ELECTRONICS

With reference to FIGS. 14a and 14b, control electronics respectivelyfor a write mode and a read mode are shown. In FIG. 14a, the lightvalves 37 (see FIG. 1 and 2) that compose each page of data and, in thisembodiment, are provided by an array of LCD elements, depicted in FIG.16c, and are addressed on a row by row basis via an address interface101 connected to an address bus 103, through an address buffer 105 and arow select switches 107 coupled directly to LCD light valves 37. As eachpage of data is composed by controlling the individual states of lightvalves 37, part of the address on bus 103 that determines the particulardata page is communicated over X and Y source select buses 109 and 111connected respectively to an X decode 113 and a Y decode 115. These inturn are connected to operate selected ones of recording light sources33, one source being located in the proper XY position to illuminate asingle data page on the recordable data layer 19. Also, taken from bus103 are data words and word count signals which are passed via businterfaces 101 to a word assembly register 117 and a timing and sequencecontrol 119. Timing and sequence control 119 is a conventionalsequencing device having outputs including clocking assembly register117 and sequential signals for "load assembled row", "row increment","pulse light source" and "done" that cooperate with row select switches107 and recording light sources 33 to sequentially load and flash eachpage of data composed at light valves 37. The intensity of light imagedthrough light valves 37 onto data layer 19 is a function of the type oflight sources 33 used and the duration and power applied to each source.For laser diodes, sufficient light energy is generated to image thepattern after being condensed through the objective lens optics onto adata layer 19 made of silver halide, dye-polymer, or a thin tellurium(Te) film. This and other materials are known per se inwrite-once-read-many (worm) records.

Once a data layer is written with multiple pages of data, such as byusing the foregoing recording processes, or in reading mass copied datacards, an addressing control such as shown in FIG. 14b is employed. Forthis purpose, addressing data from a data bus 121 is connected via aninterface bus 123 through an address buffer 125 to select particularrows of data after an image has been formed on sensor array 27. This isdone by operating row select switches 127. To illuminate a selected datapage, the address available from bus 121 includes page address data fedover X and Y decode buses 131 and 133 which cause X decode 135 and Ydecode 137 to select a particular one of the multiple light sources 15to illuminate a single page of data for imaging onto sensor array 27. Atiming control 139 similar to timing and sequence control 119 providesin a manner known per se, a sequence of timing control signalsidentified as "pulse LED" (controls page light sources 15); "pulse CCDrow" (controls the read-out of data from a charge coupled device sensorarray 27); "gate MUX" (controls an output multiplexor from sensor array27); and "data ready" (signals that the data is ready from the dataoutput multiplexor and interface to a data user bus). As described morefully below in connection with FIGS. 15a-c, the output of data fromsensor array 27 is available through a buffer register 141, amultiplexor 143, an interface to bus 145, and an output data bus 147.

SENSOR ARRAY

FIG. 15a illustrates a preferred sensor array 27 and interface circuitry29 using photosensitive elements provided by a conventional chargecoupled device (CCD) array formed in a large scale integrated circuit.Any of numerous CCD designs used in the video picture imaging field aresuitable, such as those configurations disclosed in the article byWalter F. Kosonock, CHARGE-COUPLED DEVICES-AN OVERVIEW, 1974 WesternElectron. Show and Cony. Tech. Papers, Vol. 18, Sep. 10-13, pp.2/1-2/20. Each sensor site is located to receive a data light imagerepresenting a single data bit, either "on" (1) or "off" (0) dependingupon the data pattern imaged on sensor array 27. In underlying chargestorage regions of the CCD wafer forming array 27, charge coupledelements receive the level of charge (representing the strength of lightillumination on the overlying photosensor elements 27a) and store thelevel of image data. This signal level representing data is then shiftedout and converted into binary ones and zeros by a threshold sensingoperation in the output electronics shown in FIGS. 15a, 15b and 15c.

Thus, in FIG. 15a, array 27 receives row select data from row selectswitches 127 and dumps the charge level data from each row of the storedimage into the analog buffer register 141. In conventional chargecoupled devices, analog buffer register 141 is normally outputtedserially as may be done using a serial output amplifier 152 as shown.Preferably the charge level data representing image data is withdrawn inparallel from buffer register 141 via a plurality of parallel outputamplifiers 153, one for each column of array 27. From buffer register141 via output amplifiers 153, the charge level data, which is still inanalog form, is converted to binary data by an interface circuit 145preferably incorporating a plurality of adaptive threshold networksindicated at 161. Each of adaptive threshold networks 161 serves toautomatically adjust the sensor site threshold depending on the amountof incident overlap or fringe light, i.e., light intented for adjacentsensors but partially landing on the subject sensor site. Above thethreshold, circuit 145 outputs a "1" signal and below the threshold,circuit 145 outputs a "0" bit for that corresponding sensor site. InFIG. 15b, networks 161 are shown with a centermost adaptive thresholdnetwork 161b that for illustration corresponds to the sensor site ofinterest, i.e., subject site, and includes an amplitude/sample circuit(A/S) 171 receiving a charge level signal through multiplexor 173 frombuffer register 141 (see FIG. 15c) of the sensor array. The output ofA/S 171 applies the signal level which represents the amount of lightenergy illuminating a single one of the sensor sites in array 27 to asignal node 175 which in turn is connected to a summing input of acomparator 177. Node 175 also sends this same level signal outwardly tothe laterally adjacent networks 161a and 161b in the network of circuit145 as indicated by interconnective weighted summing resistor 179 goingto the left side adjacent network 161a and another weighted summingresistor 181 going to the right hand adjacent network 161c.Additionally, at comparator 177, a subtractive node 183 receives theweighted summing resistor signal levels from each of the adjacent nodes,there being eight such adjacent nodes, via resistors 191, 192, 193, 194,195, 196, 197, and 198 as illustrated. It is observed that in thisembodiment the upper and lowermost rows of amplitude/sample circuitscorresponding to circuit 171 are needed to provide the level controlsignals from the above and below adjacent rows of sensor sites but thecomparison function provided by comparator 177 is only needed in themiddle row of adaptive threshold networks 161a, 161b and 161c. Atcomparator 177, the sum of the proportionally attentuated light signallevels from the adjacent sensors are subtracted at subtraction node 183from the primary site signal at node 175 to adjust the switchingthreshold. If the intensity of light illuminating a particular sensorand represented by a voltage at node 175 exceeds the adjusted thresholdof comparator 177, the computer outputs a binary "1". The adaptivethreshold adjustment is accomplished by collectively subtracting atsubtractive node 183 the weighted signals, then an output "1" or "0" issent on to the user bus 147 at the time of a strobe signal applied tostrobe line 149. Thus, an adaptive threshold is provided depending uponthe amount of overlap light impinging the sensor array from adjacentilluminated sensor sites, thereby greatly enhancing the reliability ofarray 27 to discriminate between true data light and overlap light fromdata imaged on adjacent sensors. The interconnective resistors areweighted either (A) weight for resistors 191, 193, 195 and 197, beingfrom those closer sensor sites immediately to the side or above orbelow; or (B) weight for the corner adjacent sites for resistors 192,194, 196 and 198, which are somewhat further away and have a lowerweight according to the fall off of light intensity with distance. Theactual values of these weighted resistors are determined empirically byimaging various data patterns on the sensor array and adjusting theresistor values for optimum selectivity.

The circuit for one of adaptive threshold sensor circuits 161 is shownin greater detail in FIG. 15c. As indicated, each circuit 161 includesan amplitude/sample circuit 171 which in turn is made up of a samplegate 171a, a reset gate 171b, a sample holding capacitor 171c, and anoutput driver 171d that develops the sampled amplitude signal at node175. Resistors 179 and 181 feed weighted proportional amounts of thislevel signal to adjacent networks 161 (see FIG. 15b). Comparator 177similarly includes a summing junction 177a, a subtractive junction 177b,and a strobed output gate 177c. That output gate 177c, shown as an ANDgate, may alternatively be a Schmitt trigger. The positive summingjunction 177a receives the same output level signal developed byamplitude/sample 171 at node 175 and from that signal level the summedinputs from adjacent nodes fed over to subtractive node 187 aresubtracted and the result is outputted through gate 177c at the time ofan output strobe signal applied to strobe lead 177d corresponding tostrobe line 149 in FIG. 15b. Another amplitude/sample circuit 172 of anetwork node 162 is shown in FIG. 15c for illustration, in this instancenetwork 162 being associated with the sensor site in the row immediatelyabove as illustrated in FIG. 15b and having one weighted (A) resistoroutput feeding one of eight comparative levels to node 187 of comparator177 for adjusting the threshold of adaptive threshold network 161b asshown in FIG. 15b.

ALTERNATE EMBODIMENTS

The foregoing embodiments represent preferred apparatus and method forwriting and/or reading optical data stored at exceedingly highdensities, on the order of 625 megabits per square inch of data layerand organized into multiple pages that may be individually selected byoptical means for high speed, large word retrieval. Numerous alternativecomponents and design details are contemplated within the scope of theinvention disclosed by way of example in the above specific preferredforms. For example, FIG. 17 shows an alternative write/read opticalmemory 210 occupying a more compact configuration than the memory 10described above (FIGS. 1 and 2).

Thus, in FIG. 17, memory 210 is mounted in a compact, read/write moduleincluding a housing 211 containing many of the same elements as in theabove described write/read embodiment, but here using reflective lightmodulators 217 to form the record image pattern. Light modulators 217are mounted along with a quarter wave plate 219 and a source imaginglens 221 in line with one optical axis of a polarizing beam splitter 223in which beam splitter 223 is situated in housing 211 between the readoptics and the sensor array similarly to beam splitter 31 of memory 10.On the opposite side of housing 211, parallel to and in line with theoptical axis of beam splitter 223 is an array of recording light sources225, replacing light sources 33 shown in memory 10 of FIG. 1.

The remaining elements of the memory are the same as memory 10 andinclude light source drivers 13', light sources 15', data layer 19', andmultiple lens array 21', together forming data lens card 17',diffractive corrector 23', field lens 25', sensor array 27' and sensorinterface circuitry 29'. Polarizing beam splitter 223 includes thediagonal beam splitting plane 227 and in this case, the beam splitter isa polarizing device so that light emitted by sources 225 is polarized asthe rays passing through the beam splitter. The light rays are thenreflected by modulators 217. The recording process of the optics ofmemory 210 are similar to that of memory 10 described above accept thatthe source imaging lens 221 needs to be only one-half as strong as lens35 and FIGS. 1 and 2 because the recording data images go through thelens twice prior to being deflected at diagonal plane 227 upwardly intothe field lens 25', corrector 23', array 21', onto the recordable datalayer 19'.

Reflective light modulators 217 may be provided by an array ofmicro-machined mirrors, but for economy of fabrication, it is preferredto use a conventional LCD array, each LCD site being individuallycontrollable to compose a page of data and using a low loss mirrorbehind the LCD page composer to reflect the image back toward theimaging lens 221 and beam splitter 223. The use of a beam splitter 223minimizes the loss of light energy, but this in turn requires the use ofa quarter wave length plate 219 between modulators 217 and imaging lens221 in order to maintain the sense of polarization through thereflection plane 227 of splitter 223. Like memory 10, each of lightsources 225 is selectively energized to record one page of data on itscorresponding page site on data layer 19'. The orientation of each ofsources 225 in the array on the side of housing 211 together with thevarious optics including source imaging lens 221 serves to direct andcondense the image to the proper lenslet and hence page site on layer19'. A variation of memory 210 shown in FIG. 17 would provide for usinga reflective data layer 19' or a transmissive data layer 19' with areflective surface on the upper side thereof to provide an alternativeto the read light sources 15' by using the light sources 225 for thedual purpose of recording and/or reading. During a read mode, individualones of light sources 225 would be turned on or pulsed at a power levelbelow the recording threshold and all of the reflective light modulators217 would be set to reflect all impinging light which in turn would becondensed to fill one of the lenslets of array 21'. The result is toreflect light off the reflective record at layer 19' which then passesdownwardly through beam splitter 223 to form the data image on sensorarray 27'.

Still another embodiment of the write/read system is shown in FIG. 18 asmemory 212. In this embodiment, the write mode is implemented by anarray of recording light sources. 251 arrayed in the pattern of a datafield to compose each page of data. Light sources 215 are here mountedto one face of a drive circuitry module 253 in which both the array ofsources 251 and circuitry 253 are flat structures such as printedcircuit cards or boards disposed within housing 255 parallel to one ofthe housing side walls adjacent a beam splitter 31'. Between beamsplitter 31' and recording light sources 251 is an array of micro lenses257 functioning as a field lens, and being carried in a set of eightelectromechanical X,Y movers serving to adjust the position of the imageforming recording rays onto the preselected data page site of data layer19' through lens array 21'. Movers 259 are shown in greater details inFIG. 19 and, as shown, eight such movers are disposed in pairs at thefour corners of field lens array 257 so as to effect X and Y translationof the array plane for moving the image into a position for preciseregistration of the source rays onto data layer 19. Movers 259 areconventional electro-magnetic transducers--e.g., moving magnetdevices--although other suitable known transducer devices for convertingelectrical positioning signals into movement may be used. These moversneed only operate at a relatively slow electromagnetic speed to set theoptics prior to the recording of each page of data composed on recordinglight sources 251. LCD or other light valve type shutters 260 screen outlenslets and hence data pages that are not to be recorded.

FIG. 21 shows another alternative embodiment in schematic form by whichdata is imaged from the data/lens system through a diffractive correctordirectly onto a sensor array without an intervening field lens. In thisembodiment, the four optical surfaces of the lenslet and diffractivecorrector are prescribed as, for example, in Table 2 above, to performthe substantially equivalent optical imaging otherwise performed by theomitted field lens of the previously described embodiment in FIG. 13,prescribed in Table 1. FIG. 22 is still another alternative embodimentof the invention again shown in schematic form depicting a data/lenssystem with the data being imaged through a field lens but omitting thediffractive corrector resulting in lower density that may be acceptablein certain applications. A higher density variation on this FIG. 22embodiment would provide diffractive gratings placed on one or both ofthe field lens surfaces in order to provide further correction of theoptical aberrations as needed to enhance resolution required by aparticular application.

FIG. 23 shows an alternative version of a write/read memory in which thesensor array is modified to incorporate both sensors and emittersdisposed in an interspersed, side-by-side by-side pattern on a commonplane. Thus, the same plane serves both to receive the imaged data forsensing, as well as an object plane to compose record data by selectivedriving of the interspersed emitters. The composed record page is thenimaged back onto the data layer through the same optics as the readimaging but in reverse, condensing fashion to write (record) onto theselected record page.

The set of FIGS. 24a, 24b and 24c shows various portions of a largescale integrated (LSI) circuit fabricated for use as the compositesensor and emitter array 315 of memory 310 described above in connectionwith FIG. 23. Thus, as shown in FIG. 24a, the array 315 includes aplurality of sensor/emitter units 315', arrayed so that all told thereexists a number S of such units equal to the number of bits that areimaged or generated at array 315 for each page or region of data layer19'. Each such sensor/emitter unit 315' includes juxtaposed sensor 321and emitter 323 arranged in approximate juxtaposition so that a lightbit imaged on unit 315' will strike sensor 321 even though some of theimaged light falls outside of the area of the sensor. Similarly, duringa write operation in which emitter 323 is energized at each unit 315',the emitted light from, in this case, the somewhat smaller area emittersurface is sufficiently located within the overall area of unit 315' tocreate a source image bit at that particular array location. In additionto the semi-conductor areas forming sensor 321 and emitter 323, eachunit 315' has integrated therewith the adaptive threshold circuit andthe interconnects to the counterpart sensors in adjacent unitscorresponding to 315' and here including drain follower 331, differenceamplifier 333, AND gate 335, and the weighting resistors 337 shownsomewhat pictorially in the diagram of FIG. 24a. In this embodiment,each sensor 321 has a separate adaptive threshold circuit that altersthe switching threshold of that particular sensor unit as a result ofthe amount of light falling on the immediately surrounding or adjacentunit sensors. The theory and operation is similar to the adaptivethreshold sensors described above in connection with the embodimentshown in FIGS. 15a-15e except that the adaptive threshold circuit andoperation is integrated with and co-functions with the operation of eachsensor site on array 315. Thus, with reference to FIG. 24b, an enlargedfragment of the sensor/emitter unit 315 is shown in aschematic/pictorial diagram to provide sensor 321 as a diode 321a, herebeing a PIN type diode but which could also be a CID (charge injectiondiode) or other photosensing element, in which the irregular polygonarea 321b depicts that surface area of the semiconductor material thatforms one electrode of the schematically indicated PIN diode 321a. Thecathode of diode 321a is then connected as indicated to MOS drainfollower 331 (corresponding to MOS drain follower 162 in FIG. 15cdescribed above). The output of drain follower 331 is then fed todifference amplifier 333 (being the counterpart of differentialamplifier 177 in. FIG. 15c described above) which performs the thresholdcomparison and outputs data through AND gate 335 for data light incidenton sensor 321. The adaptive threshold operation which effects theswitching threshold of differential amplifier 333 in conjunction withoutput diode 335 is provided by a network of weighting resistors 337which feed input signals to differencing amplifier 333 from the adjacentsensor sites in a manner similar to the operation of the weightingresistors A and B described above in connection with FIG. 15c.

In this embodiment, each unit 315' of the array also includes a lightsource here in the form of a solid state diode emitter 323. Emitter 323is shown schematically and pictorially to include an emitter 323 formedby a light emitting diode 323a and a land area 323b constituting anelectrode of the diode 323a at which photo emission occurs, forming thesource of light. The area of each unit 315' is, in this embodiment,substantially 0.03 mm by 0.03 mm square such that the entire array 315as shown in FIG. 24a will be composed of an array of 1000×1000 for atotal of 10⁶ such units.

With reference to FIG. 24c, the schematic diagram of the sensor and itsassociated adaptive threshold circuit, as well as the separate source oremitter circuit are shown to include PIN type diode sensor 321aconnected with its cathode to an MOS drain follower 331 and to an MOSreset device 337 for clearing the storage of any signal on follower 331during a read cycle. The output of drain follower 331 is fed to an input333a of difference amplifier 333. In addition to sending its outputsignal to one 333a of difference amplifier 333, follower 331 also sendsthe output signal for that particular sensor to the A and B weightingresistors 337 that are distributed to the adjacent sensor units of thearray as described above. Similarly, the comparison input 333b todifference amplifier 333 receives the weighted light sensing signalsfrom the adjacent sensor sites through the network of weightingresistors 337 to adapt or adjust the switching threshold of amplifier333 as it responds to the output of PIN diode sensor 321a throughfollower 331. An output of difference amplifier 333 thus has theswitched adaptive thresholded output signal which is applied through astrobed AND gate 335 to a user bus multiplexer representing the outputbit signal for that particular sensor site.

As a schematically separate circuit from the sensor, the photo emittingsource or diode 323a is connected across X and Y address or select leadsas shown so as to be energized whenever that particular bit of the array315 is to be illuminated for a record mode.

As an alternative to the composite sensor and emitter array 315 shown inFIGS. 24a, b and c, a similar LSI circuit may be used as a sensor-onlyarray by omitting the source or light emitter 323 from each array unit315'. In such case, the sensor area 321b, as shown in FIGS. 24a and 24b,can be enlarged to a regular rectangular shape by shifting some of theadaptive sensor circuitry components down into the space otherwiseoccupied by the source 323. Otherwise, the circuitry as schematicallyshown in FIG. 24c for the sensor portion of the array and the basicarrangement of elements shown in the plan view of this LSI circuit wouldremain the same. Another variation on the embodiment of array 315 ofFIGS. 24a, b and c is to provide at each site a single solid stateelement, using a variation of either diode 321a or diode 323a, whichserves as a dual functioning sensor and emitter in the same physicalelement. During read, the common element is operated as a sensor; duringwrite, the element is driven as an emitter to provide one bit of thepage composer.

While only particular embodiments have been disclosed herein, it will bereadily apparent to persons skilled in the art that numerous changes andmodifications can be made to the devices and method steps disclosedherein, including the use of equivalent means and steps, withoutdeparting from the spirit of the invention. For example, other opticsmay be used in place of the preferred and above described refractive anddiffractive lens subsystems, including all refractive and alldiffractive lens systems, and different combinations of refractive anddiffractive surfaces. Although a preferred form of the lens array 21uses a sheet or layer of glass for the refractive lenslets as describedabove, an alternative embodiment may use individually fabricatedlenslets mounted in a close-packed array held together by a bondingmatrix of a suitable bonding polymer. The sensor array similarly may beprovided by different structures, including a modified D-RAM array withan overlay of transparent material to allow data image light to strikesolid state junctions in the RAM memory storage elements, or bysuperposing an array of solid state photosensing elements, e.g., diodes,on top of a D-RAM array and then coupling the photodiode outputs bymetallization downward from the top photo sensing layer to a storageelement of the underlying D-RAM for each sensor site. The imaged data isthen output from the D-Ram using conventional addressing circuitry.

ADDITIONAL ALTERNATE EMBODIMENTS

Achromatizing Diffraction Lens Systems

With reference to FIG. 25, an alternative embodiment of the invention isshown in which the refractive lens surfaces used in the device of FIG.11 above are replaced by diffractive surfaces and incorporateachromatizing optics. In this color correcting or achromatizingdiffraction lens system 400, image rays from data layer 19 pass througha first diffractive surface 402, then through an anomalous or phantomlens 404 that corrects for color aberrations caused by the diffractivesurfaces, and then through a second diffractive surface 406 from whichthe imaging rays extend to the field lens (not shown in FIG. 25).

The resulting lens system has the advantage of being a diffractiveobjective system giving rise to a substantially flat field, compactdimensions and light weight. The anomalous or phantom lens 404, whichonly serves as a color correction factor, can be omitted in thoseapplications in which a narrow band light source is used, such asprovided by a laser diode. However, for those systems in which laserdiodes are too costly, LEDs and other types of light sources produce awider band of light and hence may produce undesirable aberrations ordistortions in the imaged data due to different source wavelengthsinteracting with the powerful diffractive surfaces 402 and 406. Thereason is that the rays passing through the diffractive element are"bent" (actually, diffracted) by an interaction of the groove spacingand the wavelength of the light. The angle of diffraction is a primaryfunction of the wavelength. In contrast, the chromatic aberration of arefractive lens is due to the change in the index of refraction withfrequency, a secondary effect.

The classical way to color-correct a diffractive element is to combineit with a refractive element, because the effects are in oppositedirection. Unfortunately, because the refractive effect is much smaller,the optical system to be corrected must have most of the power in therefractive lenses, leaving the diffractive elements to a roll ofcorrecting for some of the shortcomings of the refractive elements. Thatcan be a good arrangement in many instances, especially where the systemhas a large f number and/or a small field of view.

In this invention, however, the optical system has a relatively small fnumber and a large field of view for the reasons described above. If asingle refractive lens is made strong enough to correct for thechromatic error of a diffractive element in this environment, the fieldmay curve to an unacceptable extent.

An obvious solution as mentioned is to avoid color effects by using verynarrow bandwidth light sources to image the data pages. A diode laser,even a multi-mode laser, would be satisfactory. A plasma lamp might besatisfactory depending on the pressure and the gas chosen. An LED whencombined with an interference filter would work to narrow the bandwidth,but again that will rob needed intensity. The other devices mentionedare either too costly or lack intensity.

The object of this embodiment is to provide new ways to correct adiffractive lens system for color aberrations. The novel feature is toinclude one or more refractive surfaces within the system, where thesurface is the interface between two materials, in effect a buriedrefractive surface. The two materials are chosen such that the index ofrefraction is the same for both at the middle wavelength, but thedispersion is different. That is, at wavelengths different from thecenter wavelength, there will be a difference in the index, so at thecenter wavelength (or any other selected wavelength) the lens has noeffect at all; it is not there. It is a "phantom" lens. At a wavelengthdifferent from the center or selected wavelength, the lens is effective,and will act as a positive lens for wavelengths on one side of theselected one, and a negative lens on the other. Which is which dependson the sign of the curvature of the surface, and which material has thegreater dispersion. In this way, the lens corrects primarily forchromatic aberration, and has minimal effect on field flatness or otheraberrations. At a wavelength extreme there will be some effect otherthan color, but it is very small and can be neglected in thisembodiment.

In selecting a glass or plastic with a high enough dispersion to giveenough index change over a small wavelength range, the followingapproach is used. As an example, an LED that has a center wavelength of0.645 microns, has a bandwidth of about 0.02 microns. This would be thefull width at half maximum. As sources go, (not including lasers) thisis a narrow wavelength range. And the index of ordinary glasses does notchange enough over that range.

The fact that the index changes at all in normal transparent materialsis due to absorption bands that are in the infrared and in theultraviolet. It is a fact of nature that as one approaches a resonancein any system, the phase changes rapidly. In an optical system, this ismanifest as a change in the index as an absorption band edge isapproached. The index always decreases as the wavelength increases up tothe edge. On the other side of the edge, the index jumps to a highervalue, but still decreases as the wavelength continues to increase.There is a very rapid change with the opposite slope in the region ofthe band edge, but at that point the absorption is at a maximum, so thedispersion is very difficult to observe. A discussion of this effect canbe found in most physical optics texts often under the subject"anomalous dispersion", e.g., Jenkins and White, "Fundamentals ofOptics" 2d ed., p. 466, or R. W. Wood "Physical Optics" Chapter 15, 3dedition.

The implementing process for the phantom or anomalous less 404 in FIG.25 is to dissolve a dye in the plastic (glass may also be used as analternative), where the dye band edge is near the light sourcewavelength. The edge could be either above or below, but for thisembodiment, the dye is selected to be on the short wavelength side ofthe source. With the above LED chosen, the dye would be a greenabsorber, so it would appear red or purplish. Because the dye willabsorb, the thickness of the dyed material must be kept relativelysmall. This is not an optical problem, as a very thin layer can do thejob, although in a particular system there might be constructionalproblems if it is too thin.

FIG. 25 is one example of an all diffractive system that has very goodcharacteristics, except for color errors. The addition of theplanoconvex phantom lens 404 embedded in plastic between the diffractionsurfaces 402 and 406 correct for the color aberration very effectively.The lens is preferable in a Fresnel form, as best shown in FIG. 26 sothat the absorption loss would be minimized. The dispersion chosen forthe lens is thought to be reasonably attainable.

For example, as shown in the graph of FIG. 32, the index as a functionof wavelength is plotted for a dye known as Nitrosodimethylanaline. The"x" marks are taken from experimental data that are given in Wood, page508, supra. The continuous curved graph is a best match that is based onanomalous dispersion theory (see e.g., Born and Wolf, PRINCIPLES OFOPTICS, Pergamon Press, 6th Edition, p.92 eqn 31). FIG. 33 showsequation e (λ) for index as a function of wavelength (λ) for a singleoptical absorption line (band). Revised equation solved for p (which isactually n squared), and a dissipative term added as suggested at thebottom of page 92(Born and Wolf). The term 1 is the wavelength of theabsorption band center, lambda (λ) the variable. The match is notperfect, mainly because the equation assumes a single absoption line,when in fact there are usually several in a typical solid. Further,there may be other bands, particularly in the infra red, that are notaccounted for in the simple equation. However, the straight line of FIG.32 shows the dispersion required to make the phantom lens 404 work, andit should be noted that that particular dye is more than adequate from awavelength range of about 0.68 microns to 0.58 microns. The dispersionis much larger at even shorter wavelengths, but absorption would beginto have a more serious effect.

With reference to FIG. 28, another variation of the embodiment of FIGS.25-27 is shown in which the second diffractive surface 406' has beenmoved from the data lens card to the first surface of field lens 25. Theanomalous or phantom lens element 404 for color correction remainsembedded in a plastic material that is bonded to the first diffractivesurface 402 and to data layer 19 to form a data lens card.

With reference to FIG. 29, another embodiment of the anomalous orphantom lens for color correction is found in a system that provides thedata and objective lens elements as a card as in the embodiment of FIGS.25-27, but replaces the refractive field lens with an all diffractivefield lens system provided by a diffractive field lens surface 410 andanother diffractive field lens surface 412 separated by a spacermaterial of optical plastic. The advantage of this all diffractivesystem for both the objective and the field lenses is that it furtherenhances the system compactness.

FIGS. 30 and 31 illustrate an embodiment of the all diffractive lenssystem including the anomalous or phantom lens 404, here again being ofFresnel form, combined with an intervening LCD page shutter element 415including polarizing layers and being located proximate the firstobjective diffractive element 402'. For this embodiment, the data lenscard is made of data layer 19 and an optical bonding plastic on whichthe first objective diffractive surface 402' is formed as indicatedfollowed by an air space indicated at 420 separating the next system ofLCD shutters and lens elements which include shutter LCD 415, anomalouselement 404' for color correction, a second diffractive objectiveelement 406', and then first and second field diffractive elements 410and 412 all of which are held together by plastic spacer and bonding asindicated. The LCD shutter 415 is located in a region where the lightrays from adjacent pages are not overlapping, hence LCD 415 is locatedadjacent the first diffractive surface 402'. In this lens system andusing two objective diffractive elements 402' and 406', the LCD shutterelement must go after the first diffractive element so that a singlepage shutter is not distorting an image by cutting off or lettingthrough rays from adjacent pages. For this purpose, it is efficient tomake the data lens card of just the data layer 19' and the firstdiffractive element 402'. The shutter LCD 415, color corrector anomalouslens element 404', second diffractive layer 406', and the fielddiffractive 20 layers 410 and 412 are conveniently bonded together as aunit. Either air space or a solid optical plastic may be used betweenthe second diffractive field element 412 and the sensor array.

With reference to FIG. 34, still another embodiment of the lens systemis shown in which a first objective lens element is a composite ofrefractive and diffractive surfaces indicated at 430. The anomalous orcolor corrective phantom lens region 404' lies between this compositerefractive and diffractive element 430 and the second diffractivesurface 406'. By shifting some of the objective imaging power from thefirst diffractive surface into the refractive component of the compositesurfaces 430, the grating can be less fine and hence easier tofabricate, and secondarily, the amount of color correction orachromatizing is reduced and hence the prescription for the anomalous orphantom lens region 404' is less stringent, thereby permitting a widerselection of doping materials or dyes. In making these choices it isalso preferable to keep the refractive power relatively small tominimize field curvative.

GRIN Lenses Using Anomalous Dispersion Dyes

With reference to FIG. 35, another embodiment of the objective lenssystem for imaging the multiplexed data pages uses a gradient index lenssystem 450 bonded to the data layer 19 as a data lens card 452. Thecomposite card 452 includes a first diffractive lens surface or element454 followed by a second diffractive lens surface or element 456 whereinboth diffractive elements are augmented by a gradient index lens effectin the intervening optical plastic areas indicated at 458 and 460. Theadvantage of the gradient index lens or GRIN lens is to allow for thesame overall imaging power with less strong and hence less rigorousrequirements for the diffractive elements. In other words, some of theimaging power of the lens system is shifted from the diffractiveelements over to another type of optical lens element, namely thegradient index lens areas 458 and 460 of lens system 450 used in thecard 452. Simplified, the GRIN is fabricated in this instance by achange in the index of refraction of the material in the direction alongthe lens axis from the data layer toward the field lens and sensor,hence longitudinally of the lens axis. By using a base plastic, or itcan be glass, material between the diffractive elements and the datalayer, and then increasing the index of that optical materiallongitudinally (axially) from data layer toward the field lens, anoptical effect is achieved that is the functional equivalent of arefractive lens element. In this case, the device is fabricated by abuild up of different layers of increasingly higher index opticalplastics, either by selecting the stock material or by selective dopingof the layered material.

In an alternative embodiment, a GRIN lens configuration can be used inwhich the index of refraction varies as a function of radius. In fact,lenses made with a radial GRIN are widely known and used because theoptical effect is more similar to a conventional refractive sphericallens element. Thus, in the embodiment shown in FIG. 36, a lens systemthat is an alternative to the longitudinal GRIN of FIG. 35 is shownusing a radial gradient variation. In fabricating both a longitudinal(FIG. 35) and radial (FIG. 36) GRIN lens as components of the presentinvention, the following considerations apply.

A gradient index lens (GRIN lens) is an optical element where the indexof refraction of the lens material varies as a function of distance. Onetype of GRIN is known per se, and is a device shaped like a rightcylinder, with the index of refraction varied as a function of radius.It turns out that if the index decreases as the inverse square of theradius, the cylinder will function like a standard positive sphericallens. The power of the GRIN lens depends on the total change in index(the value of the proportionality constant), the length of the cylinder,and the diameter.

Known GRIN lenses are currently manufactured of glass. The glass that isused is a mixture of two or more components, where at least onecomponent is more soluble in some reagent than the others. The techniquehas been to put a glass cylinder in a leaching bath, which will removethe one component as an inverse function of the square of the distance.In this way, a GRIN lens can be made with the proper radial distributionof index.

Alternatively, and in accordance with my novel embodiment, a gradient isgenerate along the axis of an optical path which will give optical powersimilar to a conventional lens element and an example of such is used inthe embodiment of FIG. 25.

The preferred fabrication on such lenses is to diffuse a dye into aplastic base material. The dye will increase or decrease the base indexdepending on the location of the dye absorption band relative to theoperating wavelength of the optical system.

In the case of a radial index distribution, there are two ways to makean element. The first way is to immerse a plastic cylinder in a bath ofdye that is dissolved in a solvent that is compatible with the plastic.The dye will diffuse into the plastic on an inverse square basis withoutfurther arrangements. In this case, it is desired to have the lowerindex at the surface of the cylinder (for a positive lens), so a dyewould be chosen such that the absorption band is at a wavelength that islonger than the operating wave band.

Alternatively, a radial index distribution could be diffused into arelatively thin section of a cylinder by printing or paintingdye/solvent on the cross-section surface of the cylindrical section anddiffusing the dye into the plastic, as above. The process would resemblefrosting a cookie. The dye will diffuse in a radial direction as well asaxial, so the section must be thin relative to the required indexvariation, i.e., the cookie must be thin.

Note that a positive lens can be made by either reducing the index ofthe outer radii, or by increasing the index of the central regions. Thechoice depends on the available dye.

On the other hand, if longitudinal gradient is desired, it is onlynecessary to uniformly coat the section surface of a cylindrical piece,and again diffuse the dye into the plastic. There is somewhat moreflexibility in the manufacturing process in that there is no pattern toworry about, and the diffusion can take place from either side,depending on the type of dye available.

In the ray trace programs which may be used to design GRIN lenses, theindex is specified as two power series, where one independent variableis the radius, and the other is the axial (the direction of the light)distances

    n(r,z)=n.sub.0 +n.sub.s1 z+n.sub.s2 z.sup.2 +n.sub.s3 z.sup.3 + . . . +n.sub.r1 r.sup.2 +n.sub.r2 r.sup.4 +n.sub.r3 r.sup.6 . . .

Basic Relative Motion Mechanism

Separate Source and Sensor

FIG. 37 shows an alternative embodiment in the form of an optical datacard read and/or write device 510 (R/W device) in a read onlyconfiguration for a single optical data card 512. R/W device 510 has aslot 514 for introducing card 512 into R/W device 510. FIG. 38 depictscard 512 fully drawn into the internal mechanism of R/W device 510. Card512 is gripped by translation rollers; upper rollers 516a and 518acooperating with lower rollers 516b and 518b. The pairs of rollerstranslate card 512 back and forth in direction "A".

Yoke 520 is urged to translate in direction "B" by worm shift 522 whichis driven by stepper motor 524. Yoke 520 is supported by support rail526 bearing upon support wheels 528. Referring now to FIG. 39, yoke 520has an upper arm 530 and a lower arm 532. Arm 530 has at its distal endlight source means 534 while lower arm-532 has at its distal end sensormeans 536. The relative position of card 512 and light/sensor means 534and 536 is controlled by conventional devices and methods for thispurpose as well as additional features of this invention discussedherein.

Single Page Source

Still referring to FIG. 39, in one preferred embodiment, light sourcemeans 534 is a single light source 537 which illuminates a single pageof data on card 512. A sensor means 536 embodies a sensor array 538which receives light rays from single light source 537.

Single Page with Reflective Data Layer

A variation on the embodiment just described is shown in FIG. 40 whereina read/write module 540 with beam splitter 541 is located at the distalend of lower arm 532. Module 540 provides the light sources necessary toread and/or write data card 512 with a reflective layer 544 as well asthe sensor array 538. FIG. 41 shows a portion of card 512 illustrating areflective layer 544 behind data layer 546. The incorporation ofread/write module 540 obviates the need for upper ate 530.

Multiple Chapters

Both of the immediately previously described methods of reading a singlecard can be employed in a R/W device 510 that accommodates an array ofdata representing multiple cards or chapters 512 as depicted in FIGS.42A and 42B. In a preferred embodiment, light source means 534 would bea full chapter light source 548, shown in FIG. 43, which can beselectively controlled to illuminate single pages. Alternatively, insome applications a read/write module 540 could be utilized, thuseliminating the need for an overhead full chapter light source asdepicted in FIG. 42B.

Carousel

Another preferred embodiment adapts R/W device 510 into data cardcarousel reader 550 depicted in FIG. 44. Carousel 552 stores a pluralityof data cards 512. The upper portion of carousel reader 550, as shown inFIG. 45, houses R/W device 510. The lower portion of carousel reader 550houses data card transport means 553 and carousel rotation means 554.Transport means 553 may be a simple rack and pinion device as shownwhich lifts a card 512 up to a point where rollers 516 can grip the cardand further transport it into the grip of rollers 518 and proceed to beread or written to as desired. An alternative embodiment, not depicted,incorporates a transport means in the upper portion of carousel reader550 in effect would reach down and lift a data card up into contact withrollers 516, thereby permitting the overall housing size to be made morecompact.

Diffractive Lower Surface of Data Card

In all of the above described embodiments employing an R/W deviceutilizing rollers as shown in FIG. 37, an alternative formation of datacards 512 incorporates a diffractive layer in place of the lenslets 511depending from the lower surface of card 512 as shown in FIG. 39. Theadvantage of employing a flat diffractive surface, as opposed to thebumpier lenslet surface, is to enhance the smoothness of translation ofcard 512 through rollers 516a,b and 518a,b and to aid in maintaining theproper geometry relative to light sources and sensors.

Continuous or Indexed Data Tape Relative Movement

An additional preferred embodiment provides for continuous relativemovement between a medium supporting a data layer, such as a continuoustape, and corresponding light sources and sensors. FIG. 46 depicts anoverhead view of a portion of a data tape 560 with rows of data pages562. Pairs of rollers 564a,b and 566a,b assist in feeding the data tapethrough a reed module 568, shown cutaway, and maintaining flatness ofthe data tape as it passes through the module in direction "C". A lightsource strip 570 is mounted in the top of module 568 at a skew anglealpha relative the data tape edge normal direction "D". The skew anglealpha is chosen to permit light source strip 570 to span from thebeginning page in a data page row to a data page at the opposite end ofan adjacent row. A cutaway front side view of module 568 is shown inFIG. 47. Below data tape 560 is a field lens strip 572 and sensor array538. In this embodiment, lens strip 572 is canted at the same skew angleas light source 570. Reading of data tape 560 is accomplished bymultiplexing individual light sources in light source strip 570sequentially from left to right or vice versa depending on the directionof travel of the data tape. The reading of a continuously moving datatape can be accomplished by skewing the data page rows as opposed to theoptical components. By maintaining the optics elements in orthogonalrelationship to the direction of tape travel as depicted in FIG. 48, atape can be indexed and whole data page rows can be read at one timethen stepped to the next row to be read and so on.

An alternative embodiment incorporates a read/write module 540(described above and shown in FIGS. 40 and 43) so that data can berecorded on data tape 560. Although, in this embodiment, ordinarily onlya single row of data pages will be written at one time.

Tape Synchronization

In either of the data tape embodiments discussed above, continuous orindexed, synchronization of the data page on the tape with the readingmechanism may be accomplished by one of several methods.

Multi-flash Indexing

One preferred embodiment flashes the light source 570 at a high ratewhile the sensor array looks for fiducial data mark images (fiducialdata marks are discussed below in relation to FIG. 49), after the tapedrive system has transported the tape to approximately the correctposition for the next read. The tape drive system is controlled toprovide the correct overall data rate so the position of the next datapage is reasonably well known.

An example of the multi-flash technique follows. Assuming the data tapesystem is designed for TV, the data rate required is approximately 25Mbit/sec. with "ordinary" compression. Also assume the data tape is 16mm wide, a data page is 1 mm in diameter and 1 Mbits of data is storedper page, in a 1000 bit by 1000 bit array, yielding 16 Mbits/data pagerow. The suggested data rate of 25 Mbits/sec. then requires reading 1.6data page rows/sec which translates into tape movement of 1.6 mm/sec or1600 rows of bits per second. Flashing the light source at a frequencyof 6400 flashes/sec provides control of the reading of the data towithin 1/4 of a bit which is good enough for an accurate read. Since asmentioned above the overall tape position is reasonably well known, itis only necessary to begin flashing the light source in a search for thefiducial marks when the tape is within approximately 5% of the positionin which it will be stopped for about 0.6 seconds before indexing to thenext row of data pages.

For continuously moving tapes, indexing of a read operation must beaccomplished for each data page. As described above, either the lightsource or the data page rows are skewed in a continuous moving device.The operation of flashing the light source and looking for fiducialmarks is repeated in this configuration as described above.

Applying this technique to the TV data rate example described abovefollows. Again approximately 25 Mbits/sec is required. Since each datapage contains 1 Mbits, 25 pages are read each second. Since the datarows or the light source is skewed by the diameter of 1 page (1 mm) andthe tape is 16 pages (16 mm) wide the tape must advance 1.56 pagediameters (1.56 mm) to permit reading 25 Mbits of data. This rate oftape advance also translates into 1560 rows of bits per second. A flashrate of about 6250 Hz provides for indexing of about 1/4 bit which againis sufficient for an accurate read of a data page.

Separate Detectors

An alternative preferred embodiment utilizes a separate detector whichreads index marks recorded on an edge of the data tape. The markscorrespond to the locations of either rows of data pages or individualdata pages in the skewed arrangement. The index marks sensor is accurateto approximately 1/4 bit (1/4 micron). A conventional feedback mechanismutilizing the voltage generated by the mark detector controls the readfunction. An alternative to this approach incorporates double detectorsthat would register a balance across a mark thereby permitting the indexmark to be larger in size, such as 3 to 4 microns.

The multi-flash technique can also take advantage of index markspositioned at the edge of the data tape wherein the detector(s)signal(s) the imminent arrival of the page fiducial, so only a smallnumber of flashes would be required.

Fiducial Data Marks

Fiducial data marks are used for several purposes including registrationadjustment for reading or prior to writing if previously recordedfiducial data marks exist, where the adjustment is provided byelectronic and/or mechanical means as described elsewhere and for datatape synchronization. The fiducial data marks may be pre-recorded orrecorded at the same time that data pages are recorded. One preferredconfiguration of fiducial data marks 580 is shown on a single data cardin FIG. 49.

Slow Registration

The preferred embodiments may employ the aid of mechanical adjusters toachieve the necessary optical registration between the light source,data medium and sensor array elements of the invention. A typicalapplication of registration adjustment means is shown in FIG. 50. In theembodiment of FIG. 50, registration adjusters 600 are shown dependingfrom the top of a read only optical memory module 602. An optical datacard (chapter) 604 is shown being held up against a full chapter lightsource 608 by springs 606. FIG. 51 is a top view of module 10 of FIG. 50showing registration adjusters 600 in position proximate the corners ofdata card 604. Adjusters 600 are controlled via a conventional feedbackloop (not shown) to push chapter 604 along orthogonal axis "x" or "y"depending into a position of optical registration. Further, chapter 604can be urged through an angle Beta into angular alignment by adjusters600 since the force vectors generated, F1, F2, F3 and F4, do not actthrough the center of chapter 604.

FIG. 52A depicts one preferred type of registration adjuster 600. Thedevice is symmetrical about its central axis "A" and incorporates aresistive heating element 610 which Is surrounded by a flexible sheath612. The space within the sheath is filled with a wax, such as CantowaxJ, or polymer with a known coefficient of expansion during a phasechange from a crystalline state to a liquid state. While undergoing aphase change, the sheath expands as indicated by the phantom lines. Theexpanding sheath hears upon an edge of a chapter 604 as shown in FIG. 51and discussed above. An alternative to the embodiment shown in FIG. 52Ais shown in a side view in FIG. 52B and a top view in FIG. 52C.Depending on space limitations and type of application (to be discussedbelow) this embodiment may be preferable. The variation shown in topview in FIG. 52D and in side view in FIG. 52E has the added element of aperforated diaphragm 614 which is designed to only permit expansion ofadjuster 600 primarily in one direction thus concentrating the forcesand movement in a desired direction.

Another preferred embodiment of is shown in side view in FIG. 53A andpartial top view in FIG. 53B. Adjuster 600 embodies a solenoid coil 616and a translating core 618. The rounded end 620 of core 618 pushes upona beveled edge 622 of chapter 604 when the solenoid is energized. Thecomponents N_(x),y of the normal forces "N" acting in the plane ofchapter 604 provide the required orthogonal and angular registration.

Alternative embodiments to the wax filled embodiments or solenoidembodiment described above include using a heated bi-metallic strip witha predictable coefficient of expansion or a stack of piezoelectricelements to provide the forces necessary for registration.

In other embodiments, the adjusters may provide registration byadjusting the relative position of a sensor array as opposed to a datacard, or they may act upon guide means for a continuously moving orindexing data tape.

Single Chapter Fixed Registration

Another alternative to utilizing registration adjusters to shift theposition of a single chapter is to create a module with precisionreference surfaces against which a chapter is brought into contact.FIGS. 54A and 54B show such an embodiment. FIG. 54A is a partial cutawayside view of a read only module 602 showing a chapter 604 held upagainst a full chapter light source 608 by upward force springs 624.FIG. 54B shows a cutaway top view of a module 600 with front referencesurfaces 626 and side reference surfaces 628. Side spring 630 biaseschapter 604 against side references surfaces 628 while rear spring 632biases the chapter against the front reference surfaces 626.

Such a module can be constructed by precision molding processesutilizing filled polymers or metals. Alternatively a rough molded orcast part can be machined to provide the precision reference surfaces.

Solid Cube

A further alternative to the module discussed wherein a chapter may bereplaceable and module incorporates some registration means is to simplypot the elements of a functional module in polymer of appropriateoptical properties. Such a module could be used to permanently storesoftware of the type that is often accessed but not altered such as acomputer operating system.

Game Cartridge

Another preferred embodiment incorporates an array of data cards orchapters 604 into an array 634, one version of which is shown in planview in FIG. 55. Other versions of chapter arrays are shown in FIGS. 56and 57. These will be discussed in more detail below.

A preferred application of an array 634 is in a cartridge similar to thetype used in video games. A cartridge 636 is shown in a cutaway sideelevation view in FIG. 58 installed in a game player unit 638. Cartridge636 is comprised of a case 640 with a top, a bottom, sides and a front.The back of the cartridge is equipped with a door (not shown) similar tothose commonly found on VCR cassettes. Array 634 is suspended in theinterior of cartridge 636 by elastic suspension members 642 dependingfrom the front and side walls of the cartridge. Abutments 642 are moldedas part of case 640 and depend downward from the top of the case.

The game player unit 638, in addition to video display drivers and otherconventional elements, includes a player sensor array 644 of fieldlenses 646 and sensor arrays. The player sensor array is cantilevered inthe interior of player unit 638 so it can fit into the interior ofcartridge 636 underneath the chapter array 634. The player unit alsoincludes a light source array 650 with full chapter light sources. Thelight source array is flexibly cantilevered in the interior of playerunit in a position above an installed chapter array. Attached to the topof light source array 650 by living hinges 652 are pressure bars 654.The pressure bars are cooperatively connected by a pushrod 656. FIG. 59shows the pressure bars 654 from the rear of the cartridge in a fullydeployed position. Depending downwards from light source array 650 are aplurality of registration pins 658, which mate with registration holes662, and also depending downwards are a plurality of registrationsprings 660 which contact angled chapter edges 672.

FIG. 58 shows cartridge 636 fully inserted in a game player unit. Priorto insertion of a cartridge in a player unit, the light source array 650is biased upwards by biasing means 664, such as springs. Duringinsertion, the leading edge of the case top contacts flange 666 ofpushrod 656. As the pushrod is forced rearwards, the pressure bars beginto raise up and lobes 668 make contact with abutments 642. Furtherinsertion causes the pressure bars to rotate further about living hinges652 into a vertical position thus forcing light source array 650downwards in such a manner to sandwich chapter array 634 between it andplayer sensor array 644. Coincident with the downward motion of thelight source array is the passage of registration pins 658 byregistration notches 670 (shown in FIGS. 55, 56 and 57) in the chapterarray into registration holes 662 and the contact of registrationsprings 660 with angled chapter edge 672.

Refer now to FIG. 55. Registration of array 634 is accomplished asfollows. Individual chapters 604 are flexibly interconnected at theiredges to other chapters by elastomeric means 674. The flexibleinterconnection allows for smell relative movement between chapters toprovide the proper registration between each chapter and associatedlight sources, lenses and sensor arrays. Refer now to chapter "A" in thelower left hand corner and the associated registration spring "B" andregistration pins "C" and "D". During insertion of a cartridge into agame playing unit, a portion of registration spring B exerts a normalforce "N" against angled chapter edge 672. The orthogonal components ofnormal force "N" in the "x" and "y" directions urge chapter "A" againstregistration pin "D" which establishes the orthogonal registration ofchapter "A". Similarly, the component of normal force "N" directed inthe "y"0 direction urges chapter "A" against registration pin "C" whichprevents angular displacement of chapter "A" in the planar area itoccupies.

Each chapter 604 in array 634 is registered in the same manner as justdescribed. A single registration spring 660 may provide normal forces tomultiple chapters depending on where it is located in the array. Thenormal forces generated by registration springs are sufficient toovercome the tendency for the elastomeric means to restore each chapterto its pre-insertion position relative to one another. FIGS. 56 and 57are alternative embodiments of array 634 showing alternative chaptergeometry, registration spring configuration and placement of theregistration springs and pins. The registration springs may also beformed of a resilient non-permanently deforming material, such assilicon rubber, that will generate sufficient normal forces to provideadequate registration when brought into contact with an angled chapteredge.

Referring back to FIG. 58, an alternative embodiment of the cartridgeincludes a semiconductor chip 676 on array 634. Such a chip can providecontrol over the function and capabilities of separate portions of thechapter array, e.g., read only, write and read or erasing functions, aswell as providing processing, processing parameters, authorizationcodes, electronic serial numbers, ID codes or the like.

Another preferred embodiment provides for adjusting position of thesensor arrays 648 by incorporating registration adjuster means 600(discussed above). This embodiment allows for greater latitude in thetolerances of interacting registration parts such as chapter dimensionsand registration pin placement and size.

Alternative Record/Writing Embodiments

Yet another apparatus and method is described in connection with FIGS.60A through 60C for directing the recording light data page to aselected page on the data layer. This scheme uses an ultrasonic lensmodule in place of the mechanical movers 259 for the microfield lensarray shown in FIG. 18 while still providing recording light intensityof that system. Also, while the LCD shutters are retained in thepreferred form of this embodiment, certain applications may omit theshutters and rely solely on the selective light guidance of theultrasonic lens.

Thus, with reference to FIG. 60A, a write/read or write only memory 712is shown having a generally cubical shape similar to memory 212 in theabove described write/read system of FIG. 18, but here replacing themovers 259 of that embodiment with a dynamic ultrasonic lens module 715best shown in the front elevation view of FIG. 60B. Between ultrasoniclens module 715 and a data page composer consisting of recording lightsources 251' is an array of fixed field lenses 718 which are similar tothe microfield lens array 257 of the embodiment of FIG. 18, but in theembodiment of FIG. 60A, these field lenses remain stationary, relying onthe ultrasonic lens module 715 to selectively guide the recording lightfrom the recording bit sources 251' toward the selected page on datalayer 19'. In some applications the ultrasonic lens may provide all ofthe needed light directing function in which case the fixed field lenses718 can be omitted.

In accordance with the theory of ultrasonic optics, as known per es,longitudinal (i.e., compressional) ultrasonic pulse is injected into anedge of a glass plate 720 causing the density of the glass to bedynamically increased at the compressed area, hence causing the index ofrefraction to be increased. At the rarefactions, the density isdecreased and there the index of refraction also decreases. By shapingthe launched ultrasonic pulse properly, the compression forms a positivelens. And if the rarefactions are used, the lens is negative. Of course,the lens is transitory in time/position, i.e., dynamic, so theultrasonic waves must be synchronized with the desired motion of thelens through the glass. A continuous ultrasonic sine wave is introducedalong two axes X,Y of glass plate 720 by edge transducers 730 and 732(see FIG. 60B). The glass plate is placed adjacent the array of laserdiodes used as page composer of recording sources 251'. An array offixed field lenses is positioned between the light sources 251' and theglass plate 720. The sine waves are not standing waves, they areabsorbed at the opposite edge by ultrasonic absorbers 734 and 736 (FIG.60B). At any instant, there will be many points on the glass plate wherecompressions intersect. At these points, the two waves define anapproximation of a positive spherical lens.

The ultrasonic frequency applied to transducers 730, 732 is chosen sothat the wavelength of the compressions in the glass corresponds in anintegral way to the pitch of the sources, and when the compressions arein the correct location, the recording light sources are pulsed. Notethat there is a negative lens between each positive lens. With therecording light wavelength equal to the pitch, each ultrasonicallycreated lens diameter will be 1/2 the pitch. Since the source beamdiameter from recording sources 251' will be larger than 1/2 the pitchat the glass plate, the ultrasonic wavelength preferably twice as large(or an integral multiple larger). When twice as large, there will benegative lenses over adjacent sources, so that it is necessary to pulsethe sources 251' alternately to coincide with the positive lens in theglass plate 720.

The direction of the beam after the lens depends on the location of thecenter of the lens relative to the center of the source. By timing thesource light pulse a little early or late (or by shifting the phase ofthe ultrasound), the beam direction is adjusted to direct the sourcelight bit to the position of the chosen page.

Furthermore, this is a 2 dimensional system, so that a change in thesource timing causes the beam to move on a diagonal across the datacard. In order to sweep the beam in 2 dimensions to control therecording bit placement, it is necessary to change one phase plus thetiming, or change both phases with a constant source timing. In thisembodiment we change the phase to one transducer 732 and vary the timingof the recording light strobe as shown in FIG. 60C.

The objective of the system is to direct the light from each source intothe desired page microlens. Therefore each source beams met be at adifferent angle. To do this, the wavelength would be adjusted slightlyless than the source

The wavelength in the glass is a function of the temperature of theglass. Therefore the direction of the beams will depend not only on thephases and timing, which are easily controlled, but also on thetemperature. There are a number of ways to control this temperaturevariable including the disclosed feedback 756 described below.Alternatively, the temperature of the glass can be controlled with anoven or other thermal regulated module of known design for electroniccomponents. The temperature can be measured, and the phases adjustedaccording to an analytical or empirical dependence. The LED read lightsources can be used as light detectors. In the latter case the lightintensity through the data mask is compared to a reference and to theintensity through the nearest neighbor data pages. The phase andfrequency of the two ultrasonic drive circuits are then adjusted byfeedback to maximize the intensity at the desired data page.

As an example, the source pitch is given to be 30 microns, and a glasswith a velocity of 4000 m/s is used, and a wavelength of 60 microns isdesired. Then the frequency of the sinusoid driving the ultrasonictransducers is about 66.6 Mhz, with a period of shout 15 nanoseconds.The maximum full range of timing or phase adjustment will be half ofthat, 7.5 nsec, corresponding to the time width of a lens. The strengthof the lens which is set by the intensity of the ultrasonic wave is thenadjusted to give a maximum optical power.

The control end ultrasonic drive electronics is shown in FIG. 60C andincludes an oscillator source 750 generating the primary sine wave whichis then passed through an amplifier 752 to drive the X-axis transducer730 through a matching network 754. Feedback 756 responds to anacoustical sensor (transducer) on the glass opposite transducer 730 andcontrols the fundamental frequency of oscillator 750 to establish thedesired wavelength in the glass; i.e., it requires a specified phase atthe edge of the glass. Tapped from oscillator source sine wave source750, the same fundamental frequency is fed through a phase shifter 760and an initialization on/off switch 762, amplifier 764 to drive theY-axis transducer 732 via a matching network 766 as shown. Switch 762 isnormally off so that feedback 756 calibrates or initializes the circuitin response to X axis waves only. This switch is turned on whenactivated by data in register 770 and turned off after a delay 774 thatallows the ultrasonic waves to fill the glass plate. As described below,this delayed activate signal causes gate 776 to be enabled for strobingby a delay phase shifted oscillator pulse. Phase shift 760 is one of theprimary circuits for determining the lens position so as to direct therecording light bit to the desired page and this is achieved through anaddressing scheme including a page address fed to a register 770 thatincludes address bits that operate through a digital-to-analog converter772 to provide the predetermined page directing lens timing by supplyingthe desired phase shift to phase shifter 760 in accordance with theaddress. Similarly, the address in register 770 activates the "on"switch 762 and provides a delayed enable logic level to a light sourcestrobe gate 776. Also the delay 774 turns off the switch 762 after thedata has been recorded to allow reinitialization. The timing pulse togate 776 is taken from the main sine wave oscillator 750 through a fixeddelay (see ±60° phase shift in the wave forms of FIG. 60D relative tothe master oscillator wave driving the X-axis transducer). Thus, thetapped master sine wave form is fed over line 780 through another fixeddelay 782, then through a controlled time phase shift 784 which triggersa pulse generator 786 that provides the strobing or output pulse to gate776 that in turn strobes the light source associated with that lensaddress. The timing of phase shift 784 is controlled through adigital-to-analog converter 788 that is addressed by register 770 inmanner similar to the addressing of digital-to,analog converter 772controlling phase shifter 760. The data on bus 790 is fed to the pagecomposer light sources for enabling those particular light source bitsthat are to be recorded to be illuminated on the page composer. Theoutput from register 770 called lower power read, selects low power forthe lad feedback function, and/or for reading the data (rather than thenormal writing mode) when a reflection surface is provided behind thedata as described above in an alternative embodiment, thereby obviatingthe need for the usual lad read light sources.

Multiplexing The Light Sources

In the embodiments of the optical memory shown in FIGS. 1-24, each pageof data has a corresponding LED light source (or group of sourcesJointly driven) for reading the data in that page.

FIGS. 61A, 61B and 62-64 illustrate alternative embodiments to conserveon the number of light sources for lower cost applications withoutsacrificing the number of accessible pages.

This is achieved in one aspect of the invention by multiplexing thelight sources in conjunction with read LCD shutters or other lightvalving or direction function. The general scheme is to make one lightsource serve selectably several data pages.

In the embodiment of FIGS. 61A and 61B, each light source (e.g., sources800-805) is arranged to illuminate a 2×2 array of 4 pages as best Shownby source 804 illuminating one of the array of 4 pages in FIG. 61A. Amatrix of liquid crystal shutters (LCS) 810 is located close to theplane of the data pages. The LCS could be on either side of the pageplane, but in this embodiment it is on the side next to the sources800-805. Each element of the LCS array is the same size as the sourceilluminated 2×2 page array, but offset one page in both X and Y. Thatis, each square LCS element can control the light though only one pageof the four that are illuminated by a particular source as indicated byLCS control lead 820 from drivers 822. When source 804 is turned on bythe drivers 824, the LCS opened by control lead 820 selects one of 4pages for reading on the common sensor.

This arrangement would reduce the number of sources by a factor of 4,and if every other LCS element is on (in both X and Y) then for aparticular setting of the LCS, one quarter of the total data can beaccessed, one page at a time, by sequencing the sources only. The otherthree quarters of data pages can be accessed by the same sources, butafter the LCS "checkerboard" has been shifted one element in X or Y orboth.

As an example, where there are 50×50 pages in a chapter, there wouldneed to be 2500 sources on a page/source basis. In this embodiment, only625 sources are required.

In the embodiment of FIG. 62 each light source such as an LED isconnected to a light pipe or light guide 830. Each guide here is a flatwafer, roughly one half of an ellipsoid in shape, with the source at thefocal point and the truncated ellipsoid face congruent with a column ofdata pages. The outside surfaces are aluminized (reflective) so as todistribute all light to the truncated face in an efficient manner. Thethickness of each guide 830-1---n is equal to one page, and the lightfilled face of the ellipsoid would be as long as a column of pages of achapter. Between the truncated face of the guide and the pages is a setof LCS 832, where each LCS element is 1 page wide and as long as a fullrow of pages. Only one element would be on at a time. In the example ofa 50×50 page array, 50 sources and 50 LCS elements would be needed.Fifty pages could be accessed with one setting of the LCS array.

In the embodiment of FIG. 63 guides 840-1, 840-2, through 840-n are 2pages wide and each element of the LCS array 842 is one page wide and 2pages long (in the case of a 2-page wide guide), and made to overlap theguides one page. The LCS elements are wired alternately along allcolumns, so that either the even or odd ones are on. This will selectrows two at a time. The particular row is selected by the LED source.Columns are selected separately, so only one column has any openshutters at a time. In the case of, say, 50×50 pages in a chapter, therewould be 25 light sources, and 25 guides. With one setting of the LCS,the system could access 25 pages by source sequencing.

Alternatively, in FIG. 64, the guides 850A and 850B are 1/2 (but couldbe 1/3, 1/4, etc.) of the chapter dimension, with a correspondinginverse increase in the number of sources. The advantage is 2×, (or 3×,4×, etc.), increase in the number of pages that can be accessed with oneLCS 852 setting- There would be only one LCS element on (open) in eachgroup of guides.

As an alternative to the above light guides, they can be replaced byholographic beam distributor elements, known per es. Such an element isessentially a set of gratings, set at various azimuth angles andperiods. A (narrowband) light beam (source) directed into the element issplit into as many subbeams as there are gratings, and each subbeam isdirected to a specific location. The application here is to apply amatrix of LCS elements near the data pages as before. However, thepattern of the elements can be somewhat arbitrary due to the beam outputof the holographic distributor, and hence selected to simplifymanufacturing. For example, the pattern can be 5×5. In this case, for achapter as above, each element would cover 2500/25=100 pages. Now therewould be 25 gratings on each read light source, so each source woulddirect light to one specific page in each LCS element area. But only oneelement would be on at a tame, so a particular source would onlyilluminate one specific page. By sequencing the sources, 25 pages canthen be read without changing the LCS. In this case, 100 sources wouldbe required.

In the above multiple guide examples, and the holographic example, adiffractive element near each page is a desirable feature in order tofurther direct the beam in the proper page direction.

Submultiplexing Of Data Pages

With reference to FIGS. 65A-65D and 66A-66C, a read optical memoryembodiment is provided similar to the above described read memory inFIG. 3A, in which the multiple read light sources are modified so as toselectively illuminate and hence read portions of full data pages ontothe underlying sensor array. Thus in the embodiment shown in FIGS. 65Aand 65B, read light sources 860 are disposed at selected angles ofemission in groups of four as best shown in FIGS. 65A and 65D, andcombined with an array of holographic gratings, HOEs (holographicoptical element), 862, that respond to the angle of light sources 860 tocause one of four selective quadrants of the data page to be imaged onthe underlying sensor array 27. The BOB array 862 array 862 can belocated just before or just after the first surface of the lens system,and in this case is located between the first and second refractivesurfaces of lens array 21 as illustrated. The individual light sources860a, 860b, 860c and 860d are, in this embodiment, arrayed in a group offour, each group of four corresponding to a single page of the datalayer 19 and have an angle of emission canted inwardly toward a centralaxis as best shown in FIG. 65C and 65D. This angle A as shown in FIG.65B of each of the sources 860 relative to a central optical axisthrough the page lens system coax with HOE 862 to shift the imaging raysthat are formed by data layer 19 at each page so that portions of thedata page are selectively shifted on the sensor array 27 as bestillustrated in FIG. 65C and 65D. Thus, in FIG. 65C, one of four angledsources 860a, which may be provided by lads, is turned on. Imaging lightfrom source 860a in fact picks up data rays for the entire associateddata page. However, only quadrant A of the data page is imaged on sensorarray 27, the raining data page quadrants B, C and D, although partiallyilluminated by source 860a, are shifted outside the sensing area ofarray 27. Thus, a quarter of the data page is read on sensor array 27,lessening the size requirements of array 27 to only one fourth of thenumber of sensor bits as contained in the entire four quadrants of thedata page 865. In FIG. 65D, for comparison, another one of the foursources 860b is turned on causing the same data page 865 to beilluminated; however, by the coaction of the angle of source 860b andthe array of 862, quadrant B of page 865 is now imaged on sensor array27 and read in accordance with the processes described above inconnection with the main embodiments. No increase in overall density ofthe memory is achieved, but for certain applications, there is animportant reduction in the overall size of the sensor array 27 whilemaintaining the same size and density of the recorded pages in datalayer 19.

In FIG. 66A, an alternative embodiment is shown similar to the opticalmemory of FIG. 65A, but here the group of four light sources 870a, b, c,and d, are differently colored light sources or sources of the samebroad wavelength augmented by different color filters and combined witha color selective HOE 872 sandwiched between first and seconddiffractive lens elements 877 and 879. Light sources 870a, b, c, and d,can, for example, be provided by a yellow, green, red and near infra-redLRD device available from manufacturers such as Hewlitt PackardCorporation of Palo Alto, Calif.. The HOE diffractive elements in array872 shift the light rays that carry the data images as a function ofsource wavelength to achieve the selective reading of differentquadrants of the full data page 875 onto sensor array 27 as best shownin FIGS. 66B and 66C. In FIG. 66B, color source 870d acts through HOEarray 872 to image quadrant D of data page 875 onto sensor array 277while in FIG. 66C, source 870c images quantrant C onto array 27 with theremaining quadrants of data page 875 being shifted off of array 27 asillustrated.

Holograhic Beam Splitter For Multiple Read Modules Sharing Common Sensor

In the embodiment shown in FIG. 67A and 67B, a multiple read modulememory 890 is provided, formed about the essentially cube-likeconfiguration of the above read memory shown in FIG. 3A and describedabove, but here having a plurality of separate, fully implemented readmodules, R1, R2 and R3, arranged about the top and, in this case, twosides of the central image expansion region now occupied by amultiple-way holographic beam splitter 892. Beam splitter 892 isessentially of regular polygon configuration, here a cube, in which dataread from any one of multiple separate read modules R1, R2 and R3 isdirected onto common sensor array 27. Each of module R1, R2 and R3 is oflike construction shown by the cutaway of R1, including light sourcedrivers 13, light sources 15, data layer 19, lens array 21, diffractivecorrector 23, and field lens 25.

Holographic beam splitter 892 has a compound or multiple-way beamsplitting function illustrated by splitting planes 892-2 and 892-3 forthe side read modules R2 and R3 (the image from read module R1 passingthrough beam splitter 892 to sensor array 27). The read images for R2and R3 are turned 90° as illustrated onto sensor array 27, thus enablingthe same sensor array 27 to read data from any selected illuminated pagefrom any one of the multiple read modules R1, R2 and R3 withoutrequiring a separate sensor module.

In constructing the multiple-way holographic splitter 892, photopolymermaterials are used to form separate segments of the beam splitterdefined by the splitting planes 892-2 and 892-3 and after such segmentsare formed using holographic exposure techniques, known per se, theindividual pieces of cubical splitter 892 are adhesively reassembled. Toexpose the materials for forming the splitting planes, each plane isilluminated by a combined reference beam and image beam using coherentwavelength sources and each surface is formed with an operating hologramthat causes read data images from each of the read modules R1, R2 and R3to be reconstructed on the sensor array 27.

Density Increase By Color

The data record can also be composed of 2 or more layers of subtractivecolor filter material forming composite layer 19. The data consists oftransparent spots in each layer. The layers are usually presumed thin sothat the focal planes for each color substantially coincide. Lightsources of different colors are used to read and record. Each layercontains data, thus greatly increasing storage density.

In such an alternative embodiment, it is difficult to build a lenssystem that does not have any lateral chromatic aberration, i.e., theimage magnification is a secondary function of the wavelength. A shiftin magnification of as little as 0.1% could mean a mis-match of one bitbetween the data image and the sensor array.

The first part of the solution is to employ a method of recordingthrough the lens (or an equivalent lens) as described above inconnection with FIG. 1, so that the readback is automatically correctedfor magnification. But when the lens system is made up of diffractiveelements, the focal length will be inversely proportional to wavelength.with a multicolor system, the selected wavelengths might range from,say, 0.8 to 0.4 microns, a factor of 2. Such a shift in focal lengthwould distort the image.

The second part of the solution is to make one or more of thediffractive elements that make up the lens system out of binary elementsusing the same dyes that are used in the data mask. That As, thediffractive elements would be of the absorptive type (such as aclassical zone plate) where the absorptive parts are composed of asubtractive color dye. The point is that the element is only effectiveat the wavelength(s) that As absorbed by the dye. Therefore, severalelements may be stacked together, one for each color that is to be used,and where each element As designed to correctly focus specific color.The disadvantage of this approach is that absorptive diffractiveelements are not efficient, so stronger light sources or longer sensorintegration times will be required. But this may be acceptable forapplications that require higher density, and where speed is not ascrucial.

Density Increase By Depth

Again, as before, this alternative embodiment provides multiple datalayers separated by spaces that are substantially larger than the depthof focus of the lens system. Different layers of data are selected byshifting the focus. In previous art, this shifting of focus wasmechanical, i.e., an objective lens (there was only one) is moved tofocus in on the required layer. This movement can be augmented by colorselection.

With the present array system, the problem is how to select the properdata layer. Mechanical devices and/or beam splitters have disadvantagesfor this application and are not preferred.

It is preferred to use colored sources for data layer selection. Theoptical system is constructed so that longitudinal chromatic aberrationis not fully corrected. This means that the focal distance of the lenssystem will vary with wavelength. With appropriate design, the lens willfocus each separated data plane on to a single sensor on the basis ofcolor. This system is different from the multi-color record system, inthat the data planes are monochrome, probably are inverse sense, i.e.,the bits are opaque and the surrounds are transparent, and are spaced afew (3-6) microns apart.

Density Increase By Polarization

Two different sources are employed to illuminate the data, withpolarizations at right angles. Two data planes are composed ofpolarizing material also set at right angles. The bits are holes in thematerial. This technique will provide for only two data planes.

Spaced Sensor Rows

With reference to FIG. 68, an alternative embodiment of the sensor andregister array 27 is illustrated for improved readout reliability bysacrificing image density. In particular, sensor and register array 27is provided with spacing between rows of sensor elements to eliminateimage overlap in one dimension and the output data is processed from theadjacent elements in common rows by simplified processing circuit 950that subtracts out the overlap light from adjacent bits. By increasingthe space in one dimension, in this sense it's between the rows of array27, the processing circuit 950 operates on a serial data stream outputfrom parallel-to-serial register 141 to correct for inter-symbolinterference (ISI). In the illustrated embodiment, sensor and registerarray 27 uses the same array as described above in connection with FIG.15A and data from the record is stored only in alternate rows, bypassingthe intervening rows to create the desired inter-row space withoutrequiring fabrication of a different sensor array. Alternatively, thesensor and register array shown in the embodiment of FIG. 68 may bespecially made to provide a blank space between rows and that blankspace may be somewhat less than a full sensor element spacing as existsin the present embodiment but with sufficient inter-row space tosubstantially eliminate image cross-talk between adjacent data rows. Toresolve the data along each row and hence reduce image cross-talk, thedata is serially stepped out of register 141 into processor circuit 950which includes preceding and following subtraction circuits 951 and 952each being made up of a one bit delay, an attenuating resistor R and anInvertor connected to a summing junction 953 as illustrated. Data imagedon sensor and register array is sequentially down shifted through thearray into parallel-to-serial register 141 and then out shifted fromregister 141 into processing circuit 950 in which the preceding andtrailing data bits are subtracted at summing junction 953 with thecenter or desired data bit existing at the Juncture of the one bitdelays. Hence raw data signals on the preceding and trailing sensors aresubtracted from the desired data bit correcting the serial data which isoutput on lead 954 and passed on to the downstream data processing. Theattenuating resistors R are selected to cause subtraction of only afraction of the preceding and following data bits to negate the overlapof the fringes of light images that overlap the sensors on array 27. Asan example, subtracting a value of 10 percent of the full amplitude ofthe preceding and trailing data bits is suitable.

Color and/or Polarization Filtering of Overlapping Data Spots

FIG. 69A, 69B and 69C show various forms of polarizing and/or colorfiltering of adjacent sensor cells on array 27 as an embodiment of theinvention for improving reliability by reducing cross-talk betweensensor cells. Thus in FIG. 69A, a two filter scheme is illustrated inwhich like polarizing or color filters are located along the diagonalsrepresenting a greater inter-cell spacing than occurs along rows andcolumns. The two filter embodiment is constructed by overlaying thefilter array 1002 over the sensor sites of array 27 so that the centersof the circular filters in this instance are coincident with the centersof each sensor cell. A two filter screening in this manner may be byusing alternate polarizations or two different filter colors. To readout data in this embodiment, each page will be illuminated by twosequentially driven sources either differently polarized or of differentcolors and the sensors of array 27 are read in synchronization with eachsource flash. In the case of the polarization of two filter array 1002,the two types of polarizers are at 90° apart, and corresponding lightsources would have likewise a 90° or orthogonal polarization.

FIGS. 69B and 69C illustrate variations of differently colored filters,including a three color filter version in array 1004 in FIG. 69B and afour filter array 1006, again of a plurality of different colorsillustrated in FIG. 69C for even greater separation between likefiltered elements. The three and four filter versions 1004 and 1006require a corresponding number of colored light sources flashed insequence and the data read in synchronization therewith as describedabove for the two filter embodiment.

Focal Plane Lens Array

The embodiment shown in FIG. 70 enhances the precision by which the datalight rays from the imaging optics are directed onto the elements ofsensor array 27. Because the rays from the data light are striking thesensor plane at an angle that is usually not normal and because thelight rays tend to be somewhat diffracted or dispersed, this embodimentprovides a focal plane lens array 1010 provided by an array of singlesurface refractive lens elements indicated at 1012 and formed by amolding process on an optical plastic or transparent spacer 1014 thatlies flush against the sensor image plane. The bundle of light raysassociated with each data bit as depicted in FIG. 70 are refocused bythe refractive surface elements 1012 so that the refocused image bitstrikes the sensor elements squarely and with greater sharpness thanwithout the focal plane lens array 1010. The focal length of elements1012 is relatively short, on the order of the center-to-center spacingof the lens contours and hence on the same order of spacing as thesensor elements as described above. The thickness of the transparentoptical spacer 1010, which may be plastic or ordinary glass, isapproximately three to four-times the center-to-center spacing of thelens surfaces 1012; however, this spacing will change depending upon thetype of spacer material used. One advantage of this focal plane array isthat each sensor element can be made smaller, thus improving thesignal-to-noise, and leaving more room adjacent each element for on siteprocessing elements.

Field Flattener Lens at Sensor Plane

In FIG. 71, an optical system is shown in a view similar to that ofabove described FIG. 13, but with the addition of a plano concave fieldflattener lens 1020 placed up against the sensor plane of array 27 asillustrated. Also, in this embodiment, the relatively high poweredimaging optics are provided by an all diffractive array 1022 (shown forone data page only) which may utilize the all diffractive lens systemdescribed above in connection with FIG. 25. The field lens 25 remains asa refractive element. The advantage of a field flattener lens 1020 is toreduce the requirements on the imaging optics to produce a flat imagefield, in turn, the manufacturing of the imaging optics will be lessexpensive.

Alternative Embodiments of Sensor Array and Data Processor

With reference to FIGS. 72A, 72B, 72C, and 72D, an alternativeconfiguration of the sensor is shown as a large scale integrated circuitsensor array 1050 in FIG. 72A in which each sensor site or cell appearsseparately in FIG. 72B on an enlarged scale as cell 1050'. The number ofcells in array 1050 will depend on the desired data storage capacity ofthe optical memory and the resolution specifications, but as an exampleof one embodiment, an array of 512×512 IC sensor cells 1050' is formedon the sensor chip. Bach cell 1050' as depicted in FIG. 72B is shown ina further enlarged and shaded IC topographical layout in FIG. 72C andthe corresponding schematic diagram is depicted in FIG. 72D as cellschematic 1050". Each of the cells 1050' receive light data in the areaof photodiode PD1 shown by the textured region that is roughly threequarters of the overall rectangular cell site and generally centered inthe rectangle. The remaining elements, including various input andoutput metallizations as well as FET transistor gates, are shown in FIG.72C by like reference numerals in the schematic diagram 1050" of FIG.72D. Thus the FET gates appear as q1, q2, q3 and q4 in both figures andthe various input supply and output Vdd, rstn (reset), ens (enableside), and enc (enable center), gnd (ground), side and center signaloutputs also are indicated in beth figures. As explained herein, theside and center outputs, when enabled by ens and enc, respectively,produce the detected light signal in analog form as raw signalinformation by means of two isolated outputs which are used in an offsite processing of these signals to develop the corrected and processedbinary data in the manner described below. Alternatively, the processingcan be on site in the IC matrix or along the edge of the IC sensormodule chip.

In order to read information off the sensor placed in the focal plane ofthe data image, the sensor 1050 and associated signal processing decideswhere to look for each bit and then determines whether the bit value is(1) or (0). Ideally, the sensor module automatically aligns itself tothe data image, suppresses the optical intersymbol interference betweenbits, and quantizes the optical information into digital (1)s and (0)s.For this embodiment, sensor 1050 uses twice the bit density or size asthe image it is trying to discern to prevent image aliasing. Thus, foreach nominal optical data spot, a 2×2 array of four sensor cells 1050'is used.

The image is initially found by means of peak detectors, the method ofwhich is described in detail below, by searching a known area forfiducial data or special marks in the data image. Once these peakfiducial values are located, the offset and skew (rotation) of the imageare known within one sensor cell. This allows the system to locate anyparticular spot (or bit) that it chooses. When the bit value of aparticular address is desired, the processor (see FIG. 73B) adds theeffective offset value to its programmed address and examines theappropriate data levels at the sensor plane.

To suppress optical interference between bits, the processor not onlyexamines the image bit containing the information it wants, but alsolooks at neighboring bit values. Depending upon the optical spot spreadand the orientation of neighboring image bits, a percentage of each issubtracted from the bit of interest.

To quantize this analog value and convert to binary data, a threshold isset. This function is served by looking at peak current values in theregion of the cell site that is being examined. Knowing the maximumvalue and the fact that this value represents a (1) and that the minimumvalue represents a (0) yields a central current value around which adecision is made. Coding format can assure that there are (1)s and (0)snearby. This allows the processor to compensate for intensity variationacross the data image and to make the best decision for each bit basedon its environment, yielding the best signal-to-noise ratio. An exampleof the basic sensor cell used for this technique is shown by the circuitschematic of FIG. 72D that is the basic unit cell on the array. Thecircuit 1050" functions to collect photons in the photo-diode andproduce a current for processing.

The photo diode PD1 is constructed of an N+ diffusion into the substrateof the IC, commonly used for source and drain implants of the N-MOSspecies of transistor. This diode is back biased an amount equal to thepower supply voltage Vdd to maximize its depletion region volume. Apercentage of the photons striking the diode surface produceelectron-hole pairs as they pass through the depletion region and impactthe lattice. In the presence of the depletion region field, theelectron-hole pairs do not recombine, and those form a photo current.This current is integrated on the gate capacitor of q2, producing a gatevoltage proportional to the intensity of exposure and its duration. Withan applied gate voltage, q2 will conduct and pass a current from thesupply voltage.

To sense the bit value, either q3 (center) or q4 (side) is turned onwith a positive voltage. These devices act as switches to enable thephoto-proportional current potential of q2 onto one of the two sensingbuses. Depending upon whether the processor has determined that thisparticular bit is a side value or a central value determines whichenable line (ens for side, enc for center) will be turned on. When thesensing operation is complete, the enabled FET is turned off and therstn signal is driven to ground potential, discharging the gate of q2and re-establishing the full depletion region on the photo diode. Whenthis operation is complete, the rstn line is driven back to the supplyvoltage and re-exposure can occur.

Sensor Processor

With reference to FIGS. 73A and 73B, the sensor processor elementprovides an interface between the outside world and the data. Theprocessor sits on a parallel digital data bus and talks to a system CPUlike an ordinary storage device (such as RAM, ROM or a disk drive). Whenthe system CPU requests data by presenting the address and appropriatecontrol signals, the processor's actions are set in motion. The firststep is to initialize at 1062 by clearing the array of old data,effectively discharging all sensor cells to a known initial state.Having done this, the processor 1060 activates a light source,illuminating the germane data page on the record. This exposes thesensor to the data at which point the information can be accessedelectrically.

In the next phase of operation, the processor synchronizes at 1064 bydetermining where exactly on the sensor the data is imaged. This is toaccount for any mechanical misalignment that may have occurred due tofunctional tolerances (each new piece of media mounted to the readerwill have a new randomly determined alignment). To do this, theprocessor initiates a peak detector action which returns the sensoraddress of known fiducial data from several locations. This gives theprocessor relative addressing information which is used to modify theword address presented by the system CPU, thus the correct sensor datalocation may be accessed.

At this point, page data may be obtained. The relative address ispresented to the sensor from the processor and the analog informationfrom the sensor is input to the de-blurring and threshold circuitry onthe side of the sensor. This function removes any interference betweenbits and then decides whether a location contains a one or a zero. Inthis way, the processor constructs the word in a digital format. Havingdone these steps, the processor can then feed the data to the system CPUvia the data bus. If another word in the same page is requested by thesystem CPU, the processor simply goes out and accesses the desiredsensor location without re-exposing the sensor to a new data patch(page). An address on a new page requires that the sensor be cleared andthat a new data patch be imaged on the sensor.

Peak Detection

The image is aligned by means of peak detectors which go out and searcha known area for fiducial marks in the data image. Once these peakvalues are located, the offset and rotation of the image are knownwithin one sensor cell. This allows the device to locate any particularspot (or bit) that it chooses. When the bit value of a particularaddress is desired, the processor can add the effective offset value toits programmed address and examine the appropriate bits. Since imagerotation will be small, any angular calculations degenerate to linearsummations not trigonometric operations. This is due to the fact thatSin(x)=x for small x. Thus both offset and rotation can be accounted forby an offset address which varies across the image (depending upon therotational angle).

Algorithm

To suppress the optical interference between bits, the processor mustnot only examine the bits containing the information it wants, but mustalso look at neighboring bit values. Depending upon the optical spreadand the orientation of neighboring bits, a percentage of each issubtracted from the bit of interest. This may be done in several ways,such as weighted voltage summing, charge summing or current summing. Forthis discussion, current summing will be described. Presuming that bitvalues are available as currents, in a randomly accessible fashion, theprocessor can enable the central bit (the one containing the informationdesired) and subtract from it portions of the surrounding (side) bitvalues. This can be done using transimpedance amplifier configurationsor simple current mirrors. This difference yields the actual bit currentif there were no optical interference. Such an operation is inherentlyparallel since several bits need to be accessed in order to evaluate asingle bit, thus the technique can be applied to a whole word. Also,this method is best applied as the word is read out, and fortunately sosince this speeds the access time up. In actuality, three words areaccessed at once by parallel read lines. This allows the construction ofthe local neighborhood for each bit, forming the inputs required for theintersymbol interference inhibition algorithm.

Decision Making

Now with de-blurred analog information, the processor must decidewhether a bit contains a one or a zero. To quantize the signal, athreshold met be set. This function is served by looking at peak currentvalues in the region of the bit that is being discerned. Knowing themaximum value (and the fact that this value represents a one) and thatthe minimum value represents a zero yields a central current valuearound which a decision can be made. Coding format can assure that thereare ones and zeros nearby. This allows the processor to compensate forintensity variation across the image and to make the best decision foreach bit based on its environment, thereby yielding the best signal tonoise ratio. An example of the basic bit cell which can be used for thistechnique follows.

The rationale for the interconnect scheme shown in this embodiment isbest understood by considering the nature of the algorithm. Since allbits surrounding the one of interest need to be evaluated, theirinformation must be brought to the edge of the sensor array as well.Thinking in terms of a vertical orientation (with the algorithmcircuitry at the bottom of the sensor bit array), the bit values to theleft, right, top and bottom of the desired bit, must be available inaddition to the values at the corners of the 3×3 array of bits making upthe neighborhood (with the bit of interest at the center). To accomplishthis with the least amount of interconnect one can consider that thevalues above and below the central bit to have an identical impact uponthe algorithm evaluation. Thus they may be summed, and this influenceupon the weighting of their contribution can be taken into account inthe processing. Summing in this scheme is simply the addition ofcurrents, thus a single interconnect line suffices to bring out theinformation of two bits. This accounts for the labeling of side bit andthe signal name ens, for "enable side". The central bit must be broughtout uniquely, so a second line is required. The name for its enablesignal enc (for enable center) reflects this. Were these aspects of thealgorithm not true, three interconnect lines would be needed to bringout the required information. This would reduce the optical capture areaand reduce sensor chip yield.

In general, the theory of the processor is as follows. We presume a twodimensional random data source, I, passed through an effective linearspace-invariant system which models optical blurring and misalignment.The data is encoded at the baud rate of 1 symbol per unit length T,which we call one baud. However, because each symbol is read out on atwo-by-two grid, doubling the baud rate, we artificially view the inputas being placed at twice the baud rate, with a single repetition in eachdimension. This simplifies the discussion, by allowing us to formulatethe problem at a single sample rate, 2/T. This increased sampling rateis crucial to system performance, since it acts to remove spatialfrequency domain aliasing. Elimination of aliasing is required tomitigate misalignment. We write ##EQU4## where the spatial impulseresponse, h, is sampled with misalignment, and can be assumed known,after measurement in laboratory tests. These tests have shown that asingle input data symbol, read-out on a two-by-two grid, falls on aL-by-L grid, with L=6.

The required filtering can be broken down into three steps: realignmentor interpolation (INT), equalization (EQ), and matched filtering (MF).We briefly discuss the role of each filter.

Interpolation is required to correct for offset and rotation of theinput mask. This is a linear process (L), but is space variant (SV). Thespatial variation is due to the rotation, as the correctiveinterpolation would be space-invariant in the presence of offset alone.The offset problem is a common one in data communications, and isreferred to as symbol timing error. The rotation effect has nocounterpart in one-dimensional data communications.

Equalization, or deblurring or pulse sharpening, consists of providing alinear (L) filter to undo the effect of the blurring. When the blurringis space-invariant (SI), so is the filtering. If the blurring function,or optical impulse response, is known in advance through lab tests, theinverse filter can be synthesized in advance, and does not vary withposition. The optimal LSI filter depends on the system noise level andon the blurring response, and presumes that the misalignment has beencompensated.

Matched filtering is a signal processing technique used to combat randomGaussian electronic noise. In effect, it is a weight-and-sum filteracting only on all pixels that contribute to any data value. Based onthe lab tests, this will be a two-by-two grid. This filter is LSI, andcan be cascaded with the equalizer. Thus, the EQ and MF are effectivelya single filter, although they have different functions. The MF isreadout at the baud rate and is sliced or compared to a threshold tomake a hard symbol decision on the data symbol value. This data can beFEC (forward error correction) encoded, and the hard decision can beforwarded to an off-chip de-interleaver and FEC decoder as required.

Above, we have discussed the basic components of the informationretrieval process; initialization, synchronization and interpolation,equalization, and matched filtering. In order to alleviate processingcomplexity, a simplified but effective system has been developed and isdescribed in connection with FIGS. 73A, 73B and 73C.

Misregistration and skew (rotation) forces the retrieval system toresynchronize each time a new mask is inserted. To aid this process,fiducial data or markings have been placed on the mask as describedabove for mechanical registration systems and again as shown here inFIG. 73C, which are easily identified based on their unique signatureand gross location. Basically, these are data arrays 1059 that lie atthe corners of each page, but alternatively can be embedded in the datasuch as in the form of a large cross centered on the mask. By readingthe offset in the horizontal and vertical we determine misregistrationat 1064, and by reading the slope of these fiducial lines, we determinerotation. With computation of the required trig functions, andmultiplies and adds, the group of pixels surrounding information bit Ais retrieved. (See FIG. 73A). Because of the gradual slew due torotation, interpolation at 1066 of nearby intensities is used to correctfor offsets of less than one full data bit. This operation requiresscaling and adding of adjacent bits after read-out, as shown in theflowchart of FIG. 73B.

At this point, we have obtained the blurred values of data bitssurrounding group A. In fact, this consists only of the adjacent bitsmarked B in FIG. 73A, since far-out data are less relevant in thedecision making. The next step in the general procedure is deblurring orequalization, as discussed in the generic procedure. In actuality, wecombine equalization with matched filtering and thresholding to developan expedient algorithm called "bit detection" 1068 shown in FIG. 73B.

The algorithm 1068 which has been implemented is based on a judiciousapproximation to ideal equalization. All bits labeled `A` in FIG. 73Aare summed; this forming the matched filter, as the input mask is 4:1oversampled upon readout. The ideal processing in a noise freeenvironment would be the MF cascaded with the equalizer, or inversefilter. We have succeeded in approximating this filtering scheme by thatshown in the last block 1068 of FIGS. 73B, where the sum of all bits at`A` is compared to the sum of all intensity in the adjacent bits marked`B`. These bits are further scaled by a factor "t" to properlyapproximate the ideal filtering scheme. The data then is passed througha threshold determination and the result of decision block 1070 is a (1)or (0) at the corresponding address. This data reading process is nowcomplete and the data passed to a system CPU.

As will be apparent, still further alternative embodiments fall withinthe scope of this invention including the use of reading light sourcescan be one of a variety of types. The requirements are that thebandwidths should be relatively narrow, turn on and off rapidly, and inpractical applications, should be long-lived. For most applications,speed is desirable, so a high flux of photons, i.e. high power, is alsodesirable. Laser diodes would be best, and they are required for thehighest speed systems, but they are the most expensive. LEDs may be usedand those made as a monolithic array are preferred. Plasma, orelectroluminescent arrays, such as are currently available for computerdisplays, would be effective, although each element cannot, at present,provide as much power as an LED. Field emission light source arrays,currently available as prototypes, are another alternative. The lightelements can consist of a single source with an array of shuttersbetween said source and the pages. In the embodiment shown in FIGS. 24aand 24b, the light source element on the IC in combination with thephotosensor can be a silicon filament-type element which will lenditself to integration with the silicon based sensors more readily thanGaAs sources.

In alternative implementations of the write/read embodiments awavelength may be used for recording that is different from that usedfor reading. In particular, a short wavelength, e.g., blue, recordinglight, would allow smaller spots to be made because diffraction would beless. In addition, there are desirable recording materials that aresensitive only to short wavelengths, such as photopolymers, diazomaterials and energy storage crystals.

Alternatively to the storage of binary data described above, the systemcan be used to store a multiplicity of analog pictures, e.g., patterns,photographs, etc., each randomly accessible at rapid retrieval times.Each page area would contain at least one photograph or pattern. Whenthe page source is activated, a picture image is transferred to thesensor array. Each sensor of the array senses one picture element, i.e.,pixel. The sensor array would provide an analog output for each pixel inthe same manner as a TV sensor, except that pixels may be addressedrandomly or at a non-TV standard rate. These data then may be comparedor correlated with other data in a separate processor.

I claim:
 1. An optical data sensor for sensing optical data imaged on asensing plane, comprising:an array of solid state light sensor elementsdisposed for receiving imaged data; and a plurality of adaptivethreshold sensing circuit means for providing a variable, adaptive lightsensing threshold to data at each sensor element in response to receiptof light on adjacent sensor elements.
 2. The optical data sensor ofclaim 1 wherein said array of light sensor elements comprises aplurality of charge coupled devices.
 3. The optical data sensor of claim1 wherein said array of light sensor elements comprises photosensingdiodes.
 4. The optical data sensor of claim 3 wherein at least one ofsaid photosensing diodes is a PIN diode.
 5. The optical data sensor ofclaim 1 further comprising a plurality of solid state light emittersdisposed substantially in juxtaposition with said light sensor elements,and means for selectively energizing said light emitters.
 6. The opticaldata sensor of claim 1 wherein said plurality of adaptive thresholdsensing circuit means comprises variable level comparator means, saidvariable level comparator means connected to receive sensor outputsignals from predetermined subgroups of said sensor elements forchanging a threshold sensing level at each said variable levelcomparator means as a function of the amount of light incident on saidsubgroups of said sensor elements.
 7. The optical data sensor of claim 1wherein said array of solid state light sensor elements and saidadaptive threshold sensing circuit means are fabricated as an integratedsolid state circuit.
 8. A method of sensing optical data imaged on asensing plane, comprising:forming a light image of a data pattern on anarray of photo sensitive elements; outputting data from each elementwhen light in said pattern that is incident on one of said elements hasa predetermined intensity threshold; and changing said intensitythreshold in response to light incident on elements adjacent to said oneof said elements.
 9. An optical data system comprising:an optical datameans for storing data as light altering characteristics and beingorganized into a plurality (P) of juxtaposed data regions each havingcapacity to store (B) bits of data; controllable light source means forselectively illuminating at least one of said data regions of saidoptical data means; data imaging lens system having a plurality ofjuxtaposed lenslet subsystems each being formed of multiple elements andso shaped and arranged in such proximity to and in optical registrationwith a different one of said juxtaposed data regions so that the imageresolving power thereof is substantially uniform over the field of viewof that data region to form an image thereof on a common image surfacespaced from said data means and data imaging lens system and wherein atleast one element is diffractive for imaging an associated data region,and at least one element is an anomalous lens means for achromatizingthe imaging rays; sensor means having a plurality (S) of juxtaposedlight sensors arranged at said image surface for sensing data as a lightimage corresponding to an illuminated data region; and data signaloutput means coupled to said sensor means for outputting data signalsrepresenting said data of an illuminated and imaged data region.
 10. Thesystem of claim 9, wherein said anomalous lens means comprises anoptical medium containing a buried refractive surface formed by apreselected dye that has an anomalous dispersion selected to cancel outcolor aberration caused by dispersion in the diffractive element. 11.The system of claim 9, wherein said anomalous lens means is in theconfiguration of a Fresnel lens.
 12. The system of claim 9, wherein saidanomalous lens means is characterized by an optical medium havingembedded therein an optical material exhibiting a predetermined sharpchange in index of refraction as a function of wavelength.
 13. Thesystem of claim 9, wherein said anomalous lens means is formed by atleast two optical media that exhibit a predetermined net dispersion suchthat the optical power introduced thereby substantially affects coloraberration.
 14. An optical data system comprising:an optical data meansfor storing data as light altering characteristics and being organizedinto a plurality (P) of juxtaposed data regions each having capacity tostore (B) bits of data; controllable light source means for selectivelyilluminating at least one of said data regions of said optical datameans; data imaging lens system having a plurality of juxtaposed lensletsubsystems each being formed of multiple elements and so shaped andarranged in such proximity to and in optical registration with adifferent one of said juxtaposed data regions so that the imageresolving power thereof is substantially uniform over the field of viewof that data region to form an image thereof on a common image surfacespaced from said data means and data imaging lens system and wherein atleast one element is diffractive for imaging an associated data region,and at least one element is a gradient index lens means; sensor meanshaving a plurality (S) of juxtaposed light sensors arranged at saidimage surface for sensing data as a light image corresponding to anilluminated data region; and data signal output means coupled to saidsensor means for outputting data signals representing said data of anilluminated and imaged data region.
 15. The system of claim 14, whereinsaid gradient index lens means is formed by a gradient of anomalousdispersion dye varying the index of refraction longitudinally of theoptical axis.
 16. The system of claim 14, wherein said gradient indexlens means is formed by a gradient of anomalous dispersion dye varyingthe index of refraction radially of the optical axis.
 17. An opticaldata system comprising:an optical data means for storing data as lightaltering characteristics and being organized into a plurality (P) ofjuxtaposed data regions each having capacity to store (B) bits of data;controllable light source means for selectively illuminating at leastone of said data regions of said optical data means; data imaging lenssystem having a plurality of juxtaposed lenslet subsystems each beingformed of multiple elements and so shaped and arranged in such proximityto and in optical registration with a different one of said juxtaposeddata regions so that the image resolving power thereof is substantiallyuniform over the field of view of that data region to form an imagethereof on a common image surface spaced from said data means and dataimaging lens system; sensor means having a plurality (S) of juxtaposedlight sensors arranged at said image surface for sensing data as a lightimage corresponding to an illuminated data region and having adaptivethreshold sensing circuit means for providing a variable, adaptive lightsensing threshold to data images incident on each of said sensorswherein said adaptive threshold sensing circuit means comprises anintegrated circuit sensor array having a plurality of subarrays ofgrouped sensor cells for detecting a single light image bit and sensorprocessing means for detecting data bits from said light image bits; anddata signal output means coupled to said sensor means for outputtingdata signals representing said data of an illuminated and imaged dataregion.
 18. The optical data system of claim 17,wherein each of saiddata regions has fiducial data stored thereon for registering the lightimage on said sensor means, and wherein said adaptive threshold sensingcircuit comprises processing means for reading said fiducial data andcontrolling addressing of said data signal output means for adapting thereading of data from said sensor means according to said fiducial data.19. An optical data system comprising:an optical data means for storingdata as light altering characteristics and being organized into aplurality (P) of juxtaposed data regions each having capacity to store(B) bits of data; controllable light source means for selectivelyilluminating at least one of said data regions of said optical datameans; data imaging lens system having a plurality of juxtaposed lensletsubsystems each being formed of multiple elements and so shaped andarranged in such proximity to and in optical registration with adifferent one of said juxtaposed data regions so that the imageresolving power thereof is substantially uniform over the field of viewof that data region to form an image thereof on a common image surfacespaced from said data means and data imaging lens system; sensor meanshaving a plurality (S) of juxtaposed light sensors arranged at saidimage surface for sensing data as a light image corresponding to anilluminated data region and means for submultiplexing data from each ofsaid data regions so as to cause portions of each of said regions to beselectively imaged on said sensor means; and data signal output meanscoupled to said sensor means for outputting data signals representingsaid data of an illuminated and imaged data region.
 20. An optical datasystem comprising:an optical data means for storing data as lightaltering characteristics and being organized into a plurality (P) ofjuxtaposed data regions each having capacity to store (B) bits of data;controllable light source means for selectively illuminating at leastone of said data regions of said optical data means; data imaging lenssystem having a plurality of juxtaposed lenslet subsystems each beingformed of multiple elements and so shaped and arranged in such proximityto and in optical registration with a different one of said juxtaposeddata regions so that the image resolving power thereof is substantiallyuniform over the field of view of that data region to form an imagethereof on a common image surface spaced from said data means and dataimaging lens system and a field flattener lens means for correctingspherical aberration of said light image incident on said sensor means;sensor means having a plurality (S) of juxtaposed light sensors arrangedat said image surface for sensing data as a light image corresponding toan illuminated data region; and data signal output means coupled to saidsensor means for outputting data signals representing said data of anilluminated and imaged data region.
 21. An optical data systemcomprising:an optical data means for storing data as light alteringcharacteristics and being organized into a plurality (P) of juxtaposeddata regions each having capacity to store (B) bits of data;controllable light source means for selectively illuminating at leastone of said data regions of said optical data means; data imaging lenssystem having a plurality of juxtaposed lenslet subsystems each beingformed of multiple elements and so shaped and arranged in such proximityto and in optical registration with a different one of said juxtaposeddata regions so that the image resolving power thereof is substantiallyuniform over the field of view of that data region to form an imagethereof on a common image surface spaced from said data means and dataimaging lens system, and a focal plane lens array after said pluralityof juxtaposed lenslet subsystems and proximate said common image surfacefor refocusing each imaged data region onto said common image surface;sensor means having a plurality (S) of juxtaposed light sensors arrangedat said image surface for sensing data as a light image corresponding toan illuminated data region; and data signal output means coupled to saidsensor means for outputting data signals representing said data of anilluminated and imaged data region.
 22. An optical data recording andretrieval system comprising:read light source array means; optical datarecord means disposed proximate to said read light source array meansfor being illuminated thereby; lens array means comprising a pluralityof substantially similar lenslets arrayed in a lens structure disposedproximate and affixed to said optical data record means, each saidlenslet forming a distal image of a portion of said optical data recordmeans illuminated by said read light source array means; light sensorarray means disposed to receive said image of said portion of saidoptical data record means illuminated by said read light source means,said sensor array means responding to said image to output data; andrecording light data composer means for producing a recording light datapattern and imaging same onto said optical data record means for storingsaid data pattern, wherein said recording light data composer meanscomprises ultrasonic lens means for controllably directing said datapattern and imaging it onto said optical data record.
 23. The opticaldata system of claim 19, wherein said controllable light source meanscomprises at least one light guide means for jointly illuminating asubset of said data regions, and electrically controlled shutter meansdisposed in a data image path between said light guide and said sensormeans for shuttering image light from certain but not all of said subsetof said data regions.
 24. An optical data reading system comprising:atleast one of an optical data storage medium with juxtaposed data regionsthereon; a controllable light source means for selectively illuminatinga data region on said data storage medium; a data imaging lens meanshaving a plurality of juxtaposed lenslets proximate said data storagemedium being shaped and arranged to form an image of an associated dataregion on a common image surface; and a sensor means having a pluralityof juxtaposed light sensors arranged at said common image surface forsensing data as a light image corresponding to an illuminated dataregion, wherein the relative positions of said optical data storagemedium, said controllable light source means, said data imaging lensmeans and said sensor means are controllably moveable in substantiallyparallel planes.
 25. An optical data reading system comprising:asubstantially planar optical data storage medium with juxtaposed dataregions thereon wherein said data storage medium is controllably movablewithin a first planar area occupied by it; a plurality of juxtaposedlenslets proximate a first side of said data storage medium being shapedand arranged to form an image of an associated data region on a commonimage surface spaced from said first side; a controllable light sourcemeans for selectively illuminating a data region of said data storagemedium wherein said controllable light source means is controllablymoveable within a second plane parallel to said first plane, and asubstantially planar sensor means having a plurality of juxtaposed lightsensors arranged at said common image surface for sensing data as alight image corresponding to an illuminated data region wherein saidsensor means is cooperatively connected to said light source means. 26.An optical data system comprising:an optical data means for storing dataas light altering characteristics and being organized into a plurality(P) of juxtaposed data regions each having capacity to store (B) bits ofdata, said optical data means defining a plane; controllable lightsource means for selectively illuminating at least one of said separatedata regions of said optical data means; data imaging lens means havinga plurality of juxtaposed lenslets each being shaped and arranged insuch proximity to and in optical registration with a separate one ofsaid juxtaposed data regions so that the image resolving power thereofis substantially uniform over the field of view of that data region toform an image thereof on a common image surface spaced from said datameans and lens means; sensor means having a plurality (S) of juxtaposedlight sensors arranged at said image surface for sensing data as a lightimage corresponding to an illuminated data region; data signal outputmeans coupled to said sensor means for outputting data signalsrepresenting said data of an illuminated and imaged data region; andregistration adjustment means being controlled by a control signal foradjusting the position of said optical data means within said plane formaintaining optical registration of said light image and said sensormeans.
 27. An optical data cartridge reading system comprising:acartridge including a housing, said housing suspending in its interior adata array of substantially planar optical data storage medium withjuxtaposed data regions thereon, said data array including a pluralityof juxtaposed lenslets proximate a first side of said data array beingshaped and arranged to form an image of an associated data region on acommon image surface spaced from said first side, a reading unitincluding a controllable light source means for selectively illuminatinga data region from a second side of said data array wherein said lightsource means is supported by said reading unit in a plane parallel tosaid data array, said reading unit further including a sensing array ofsubstantially planar sensor means having a plurality of juxtaposed lightsensors arranged at said common image surface for sensing data as alight image corresponding to an illuminated data region wherein saidsensing array is supported by said reading unit in a plane parallel tosaid data array a clamping means including registration means mountedwithin said reading unit for clamping said data array and said pluralityof lenslets between said light source means and said sensing array. 28.An optical data sensor for sensing optical data imaged on a sensingplane, comprising:an array of solid state light sensor elements disposedfor receiving imaged data; and a plurality of adaptive threshold sensingcircuit means for providing a variable, adaptive light sensing thresholdto data at each sensor element in response to receipt of light onadjacent sensor elements wherein said plurality of adaptive thresholdsensing circuit means comprises variable level comparator means, saidvariable level comparator means connected to receive sensor outputsignals from predetermined subgroups of said sensor elements forchanging a threshold sensing level at each said variable levelcomparator means as a function of the amount of light incident on saidsubgroups of said sensor elements.